Light-emitting device

ABSTRACT

A flexible device with fewer defects caused by a crack is provided. A flexible device with high productivity is also provided. Furthermore, a flexible device with less display failure even in a high temperature and high humidity environment is provided. A light-emitting device includes a first flexible substrate, a second flexible substrate, a buffer layer, a first crack inhibiting layer, and a light-emitting element. A first surface of the first flexible substrate faces a second surface of the second flexible substrate. The buffer layer and the first crack inhibiting layer are provided over the first surface of the first flexible substrate. The buffer layer overlaps with the first crack inhibiting layer. The light-emitting element is provided over the second surface of the second flexible substrate.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device, andparticularly to a flexible display device capable of performing displayalong a curved surface. One embodiment of the present invention alsorelates to a light-emitting device, and particularly to a flexiblelight-emitting device capable of performing light emission along acurved surface.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. In addition, one embodimentof the present invention relates to a process, a machine, manufacture,or a composition of matter. Specifically, examples of the technicalfield of one embodiment of the present invention disclosed in thisspecification include a semiconductor device, a display device, alight-emitting device, an electronic device, a method for driving any ofthem, and a method for manufacturing any of them.

BACKGROUND ART

In recent years, a flexible device has been developed; in the flexibledevice, a semiconductor element, a light-emitting element, and the likeare provided over a flexible substrate. Typical examples of the flexibledevice include, as well as a lighting device and an image displaydevice, a variety of semiconductor circuits including a semiconductorelement such as a transistor.

As a method of manufacturing a semiconductor device including a flexiblesubstrate, the following technique has been developed: a semiconductorelement such as a thin film transistor (TFT) is formed over a supportsubstrate (e.g., a glass substrate or a quartz substrate), and then thesemiconductor element is transferred to a flexible substrate. Thistechnique needs a step of separating a layer including the semiconductorelement from the support substrate.

For example, Patent Document 1 discloses a separating technique usinglaser ablation as follows. A separation layer formed of amorphoussilicon or the like is formed over a substrate, a layer to be separatedis formed over the separation layer, and the layer to be separated isbonded to a transfer body with a bonding layer. The separation layer isablated by laser irradiation, so that peeling occurs in the separationlayer.

Patent Document 2 discloses a separating technique as follows. A metallayer is formed between a substrate and an oxide layer and peeling isperformed at the interface between the oxide layer and the metal layerby utilizing weak bonding at the interface, so that a layer to beseparated and the substrate are separated from each other.

REFERENCES Patent Documents

[Patent Document 1] Japanese Published Patent Application No. H10-125931

[Patent Document 2] Japanese Published Patent Application No.2003-174153 Disclosure of Invention

In the case where peeling is performed between a separation layerprovided over a substrate and a layer to be separated (hereinafter alsoreferred to as a buffer layer) formed over the separation layer, a stackof thin films (e.g., the layer to be separated, a thin film transistor,a wiring, and an interlayer film) is provided over the separation layer.The stack has a thickness of several micrometers or less and is veryfragile in some cases. When peeling is performed between the separationlayer and the layer to be separated, a high bending stress is applied toan end portion of the substrate (a separation starting point); as aresult, breaking or cracking (hereinafter, collectively referred to as acrack) easily occurs in the layer to be separated.

To improve the productivity of flexible light-emitting devices, it ispreferable that a plurality of light-emitting devices be manufactured ata time over a large substrate and the substrate be divided with ascriber or the like. At this time, due to stress applied when thesubstrate is divided, a crack might occur in a thin film in an endportion of the substrate, particularly in the layer to be separated.

In addition, when the flexible light-emitting device that ismanufactured in the aforementioned separating and dividing steps is heldin a high temperature and high humidity environment, the crack, whichhas occurred in the end portion of the layer to be separated in theseparating and dividing steps, develops in some cases. The developmentof the crack reduces the reliability of light-emitting elements in thelight-emitting device, or some of the light-emitting element emit nolight because of the crack reaching the light-emitting elements.

In view of the above, an object of one embodiment of the presentinvention is to provide a flexible light-emitting device with fewerdefects caused by a crack. Another object is to provide a flexiblelight-emitting device with high productivity. Still another object is toprovide a light-emitting device with high reliability.

Alternatively, an object of one embodiment of the present invention isto provide a novel light-emitting device. Another object of oneembodiment of the present invention is to provide a lightweightlight-emitting device. Still another object of one embodiment of thepresent invention is to provide a light-emitting device that is lesslikely to be broken. Still further object of one embodiment of thepresent invention is to provide a thin light-emitting device.

In one embodiment of the present invention, there is no need to achieveall the objects. Note that the description of these objects does notdisturb the existence of other objects. Other objects will be apparentfrom and can be derived from the description of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention is a light-emitting deviceincluding a first flexible substrate, a second flexible substrate, afirst buffer layer, a first crack inhibiting layer, and a light-emittingelement. A first surface of the first flexible substrate faces a secondsurface of the second flexible substrate. The first buffer layer and thefirst crack inhibiting layer are provided over the first surface of thefirst flexible substrate. The first buffer layer overlaps with the firstcrack inhibiting layer. The light-emitting element is provided over thesecond surface of the second flexible substrate.

In the above light-emitting device, it is preferable that the firstbuffer layer include an inorganic material, the light-emitting elementinclude a light-emitting organic compound, and the first crackinhibiting layer include one of a conductive material and a resinmaterial and be positioned between the light-emitting element and an endportion of the first flexible substrate when seen from a directionperpendicular to the first surface.

In the above light-emitting device, it is preferable that a firstbonding layer be provided between the first flexible substrate and thefirst buffer layer, and a second bonding layer and a second buffer layerbe provided between the second flexible substrate and the light-emittingelement.

In the above light-emitting device, it is preferable that a layer beprovided over the first surface of the first flexible substrate, and thelayer serve as a marker and include the same material as the first crackinhibiting layer.

In the above light-emitting device, it is preferable that alight-blocking layer be provided over the first surface of the firstflexible substrate, and the light-blocking layer have a function ofblocking light from the light-emitting element and include the samematerial as the first crack inhibiting layer.

In the above light-emitting device, it is preferable that a cover layerbe provided over the first surface of the first flexible substrate, thecover layer include a portion covering the first crack inhibiting layer,and the cover layer include a conductive material or a resin materialand be positioned between the light-emitting element and an end portionof the first flexible substrate when seen from a direction perpendicularto the first surface.

In the above light-emitting device, it is preferable that a second crackinhibiting layer be provided over the second surface of the secondflexible substrate, and the second crack inhibiting layer include aconductive material or a resin material and be positioned between thelight-emitting element and an end portion of the first flexiblesubstrate when seen from a direction perpendicular to the first surface.

Another embodiment of the present invention is a light-emitting moduleincluding a touch sensor over a third surface of the first flexiblesubstrate or a fourth surface of the second flexible substrate in thelight-emitting device with any of the above structures. The thirdsurface is an opposite surface of the first flexible substrate, and thefourth surface is an opposite surface of the second flexible substrate.

Note that the light-emitting device in this specification includes, inits category, a display device using a light-emitting element.Furthermore, the light-emitting device may be included in a module inwhich a light-emitting element is provided with a connector such as ananisotropic conductive film or a tape carrier package (TCP), a module inwhich a printed wiring board is provided at the end of a TCP, and amodule in which an integrated circuit (IC) is directly mounted on alight-emitting element by a chip on glass (COG) method. Thelight-emitting device may also be included in lighting equipment or thelike.

According to one embodiment of the present invention, a flexiblelight-emitting device with fewer defects caused by a crack can beprovided. Alternatively, a flexible light-emitting device with highproductivity can be provided. A light-emitting device with highreliability can also be provided.

According to another embodiment of the present invention, a novellight-emitting device can be provided. Alternatively, a lightweightlight-emitting device can be provided. A light-emitting device that isless likely to be broken can also be provided. Still alternatively, athin light-emitting device can be provided. Note that the description ofthese effects does not disturb the existence of other effects. Oneembodiment of the present invention does not necessarily achieve all theobjects listed above. Other effects will be apparent from and can bederived from the description of the specification, the drawings, theclaims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate a structure example of a display device ofone embodiment;

FIGS. 2A to 2D illustrate a structure example of a display device of oneembodiment;

FIGS. 3A to 3C illustrate a method for manufacturing a display device ofone embodiment;

FIGS. 4A and 4B illustrate a method for manufacturing a display deviceof one embodiment;

FIGS. 5A and 5B illustrate a method for manufacturing a display deviceof one embodiment;

FIGS. 6A and 6B illustrate a method for manufacturing a display deviceof one embodiment;

FIG. 7 illustrates a structure example of a display device of oneembodiment;

FIG. 8 illustrates a method for manufacturing a display device of oneembodiment;

FIG. 9 illustrates a structure example of a display device of oneembodiment;

FIG. 10 illustrates a structure example of a display device of oneembodiment;

FIGS. 11A and 11B illustrate a structure example of a display device ofone embodiment;

FIG. 12 illustrates a structure example of a display device of oneembodiment;

FIGS. 13A and 13B illustrate a structure example of a display device ofone embodiment;

FIGS. 14A to 14C illustrate a structure example of a light-emittingdevice of one embodiment;

FIGS. 15A to 15C illustrate structure examples of an electronic deviceof one embodiment;

FIGS. 16A to 161 illustrate structure examples of an electronic deviceof one embodiment;

FIGS. 17A to 17C illustrate structure examples of a lighting device ofone embodiment;

FIGS. 18A and 18B are respectively an optical micrograph and across-sectional view of Example;

FIGS. 19A and 19B are respectively an optical micrograph and across-sectional view of Example;

FIG. 20 is a transmission electron microscopy image of Example; and

FIG. 21 illustrates a method for manufacturing a display device of oneembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below.

Note that in the structures of the present invention described below,the same portions or portions having similar functions are denoted bythe same reference numerals in different drawings, and the descriptionthereof is not repeated in some cases. Furthermore, the same hatchingpattern is applied to portions having similar functions, and theportions are not especially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, embodiments of the invention are notlimited to such scales.

Note that ordinal numbers such as “first” and “second” in thisspecification and the like are used in order to avoid confusion amongcomponents, and the terms do not limit the components numerically.

Embodiment 1

In this embodiment, an example of a structure and a manufacturing methodof an image display device, which is an example of a light-emittingdevice of one embodiment of the present invention, will be describedwith reference to drawings. As an example of the image display device,an image display device (hereinafter, also referred to as displaydevice) including an organic electroluminescence (EL) element will bedescribed below.

[Structure Example of Display Device]

FIG. 1A is a schematic top view of a display device 100 with a topemission structure. Note that in FIG. 1A, some components are notillustrated for clarity.

FIG. 1B is a schematic cross-sectional view of FIG. 1A along line A1-B1passing through a region including one of the four corners of the secondsubstrate 101, along line C1-D1 passing through part of a displayportion 102, and along line E1-F1 passing through a region including asignal line driver circuit 103 and an external connection terminal 105.

The display device 100 includes, over a top surface of the secondsubstrate 101, the display portion 102, the signal line driver circuit103, a scan line driver circuit 104, and the external connectionterminal 105.

In the display device 100, a crack inhibiting region 110 is provided tosurround the display portion 102. In addition, markers 124 are providedat the four corners of a first substrate 121.

Here, the crack inhibiting region 110 includes at least one crackinhibiting layer that will be described later.

In the display device 100, the first substrate 121 and the secondsubstrate 101 face each other with a sealing layer 153 and a sealant 154interposed therebetween. A first buffer layer (also referred to as alayer to be separated, and hereinafter simply referred to as a bufferlayer) 120 is provided on the first substrate 121 with a bonding layer125 interposed therebetween. The crack inhibiting region 110 including aplurality of first crack inhibiting layers (hereinafter simply referredto as crack inhibiting layers) 122, and the like are provided in contactwith the buffer layer 120. Furthermore, a second buffer layer 132 isprovided over the second substrate 101 with a bonding layer 131interposed therebetween. A light-emitting element 114 functioning as adisplay element, transistors included in the display portion 102, thesignal line driver circuit 103, the scan line driver circuit 104, andthe like, and the external connection terminal 105 are provided over thesecond buffer layer 132.

Note that the first substrate 121 and the second substrate 101 arepreferably flexible substrates.

The buffer layer 120 and the second buffer layer 132 inhibit diffusionof impurities that have passed through the substrates (the firstsubstrate 121 and the second substrate 101) and the bonding layers (thebonding layers 125 and 131), to the light-emitting element 114 and thelike. In particular, the buffer layer 120 over the light-emittingelement 114 increases the reliability of the display device 100.

The buffer layer 120 serves as a barrier film preventing diffusion ofimpurities to the light-emitting element 114. The buffer layer 120 canbe, for example, a single film or layered films of an inorganicmaterial. The use of such a material increases the moisture-proofproperty of the display device even when the first substrate 121 is madeof a material having a low barrier property, particularly a lowmoisture-proof property.

However, brittle fracture easily occurs in the inorganic film, whichmight cause a crack in the buffer layer 120 when, for example, thedisplay device 100 is bent. In addition, the inorganic film with lowmoisture permeability has a low swelling ratio; therefore, in the casewhere, for example, the display device 100 is placed in a hightemperature and high humidity environment, a layer in the vicinity ofthe buffer layer 120 swells more than the buffer layer 120. This leadsto stress concentration at the interface between the buffer layer 120and the adjacent layer, causing a crack in some cases.

Hence, the crack inhibiting layers 122, which are made of a materialdifferent from that of the inorganic film included in the buffer layer120, are provided in contact with the buffer layer 120. As a result, thedevelopment of the crack generated in the buffer layer 120 can behindered.

The crack inhibiting layers 122 are preferably formed using a conductivefilm that has higher ductility and a lower swelling ratio than theinorganic film.

Furthermore, the crack inhibiting layers 122 are preferably formed of aresin material that has high adhesion to the inorganic film, in whichcase stress concentration on the surface of the buffer layer 120 can bereduced at the interface between the crack inhibiting layers 122 and thebuffer layer 120.

The crack inhibiting region 110 includes the two crack inhibiting layers122. As illustrated in FIG. 1A, each of the crack inhibiting layers 122is a closed curve (also referred to as a loop or a curve with the endstouching) when seen from above, by which the display portion 102 issurrounded.

By thus providing the crack inhibiting region 110 so as to surround thedisplay portion 102, in the case where a plurality of display devices100 are manufactured at a time over a large substrate and then dividedinto each, a crack generated in an end portion of the buffer layer 120can be prevented from developing across the crack inhibiting region 110.

In addition, the display device 100 can be manufactured through the stepof separating a support substrate as described later. In that case, acrack might be generated in the buffer layer 120 as the separationproceeds from an end portion of the substrate; however, the crack can beprevented from developing across the crack inhibiting region 110.

Note that the crack inhibiting region 110 is not necessarily provided tobe a closed curve and may be divided into plural lines, though the crackinhibiting region 110 in FIG. 1A is a closed curve surrounding thedisplay portion 102.

FIG. 2A is a schematic top view of the display device 100 in which thecrack inhibiting region 110 includes, for example, the three crackinhibiting layers 122. FIG. 2B is an enlarged schematic top view of part(surrounded by a dashed line) of the crack inhibiting region 110 in FIG.2A.

A crack tends to linearly develop from an end portion of the displaydevice 100 to the inside as indicated by a dashed-dotted arrow in FIG.2A. Therefore, instead of the structure in FIG. 2B in which the crackinhibiting layers 122 are closed curves, the crack inhibiting layers 122preferably have a structure in which cut portions are provided inpositions different from each other as illustrated in FIG. 2C, in whichcase the development of a crack can be hindered without increasing thestiffness of the display device 100. Furthermore, all the crackinhibiting layers 122 which have cut portions are not necessarilydisposed perpendicularly to the direction where the crack develops; forexample, the crack inhibiting layers 122 may be arranged as illustratedin FIG. 2D.

The markers 124 in contact with the buffer layer 120 serve as scribemarkers in this structure example, though they may have a differentfunction.

For example, the markers 124 may be alignment markers used for alignmentin the deposition of an EL layer or bonding of support substratesdescribed in the later example of a manufacturing method. In the casewhere a plurality of display devices 100 are manufactured at a time overa large substrate, the alignment markers may be arranged outside a lineat which the display devices 100 are divided into each.

Other components of the display device 100 will be described below withreference to FIG. 1B.

The external connection terminal 105 is preferably formed using the samematerial as a conductive layer included in the transistors (transistors111, 112, and 113) or the light-emitting element 114 of the displaydevice 100, in which case the manufacturing process can be simplified.In this structure example, the external connection terminal 105 isformed using the same material as a first electrode 143 and an electrode136 which forms a source or drain electrode of the transistor. A signalcan be input to the display device 100 when a flexible printed circuit(FPC) or an IC is mounted on the external connection terminal 105 via ananisotropic conductive film (ACF), an anisotropic conductive paste(ACP), or the like. In this structure example, an FPC 155 is providedvia a connector 156.

FIG. 1B illustrates an example where the signal line driver circuit 103includes the transistor 111. The signal line driver circuit 103 may be,for example, a circuit in which an n-channel transistor and a p-channeltransistor are used in combination, or a circuit that is formed ofeither n-channel transistors or p-channel transistors. The same appliesto the scan line driver circuit 104. Furthermore, this structure exampleshows a structure in which the signal line driver circuit 103 and thescan line driver circuit 104 are formed over the second buffer layer 132over which the display portion 102 is formed. Alternatively, forexample, a driver circuit IC may be used as the signal line drivercircuit 103, the scan line driver circuit 104, or both and the drivercircuit IC may be mounted on the second substrate 101 by a chip on glass(COG) method or a chip on film (COF) method; alternatively, a flexibleprinted substrate (FPC) provided with the driver circuit IC by the COFmethod may be mounted on the second substrate 101.

FIG. 1B illustrates a cross-sectional structure of one pixel as anexample of the display portion 102. The pixel includes the switchingtransistor 112, the current control transistor 113, and the firstelectrode 143 electrically connected to one of the pair of electrodes136 of the current control transistor 113. An insulating layer 144 isprovided to cover an end portion of the first electrode 143.

In this example, the transistors (111, 112, and 113) in the displaydevice 100 are bottom-gate transistors. Each of the transistors includesa semiconductor layer 135 having a region serving as a channel, a gateelectrode 133, and an insulating layer 134 serving as a gate insulatinglayer. Moreover, the pair of electrodes 136 are provided in contact withthe semiconductor layer 135, and an insulating layer 141 and aninsulating layer 142 are provided to cover the semiconductor layer 135and the electrodes 136. Note that in the semiconductor layer 135,low-resistance regions may be provided with the region serving as achannel interposed therebetween.

The light-emitting element 114 has a layered structure in which thefirst electrode 143, an EL layer 151, and a second electrode 152 arestacked in this order over the insulating layer 142. Since the displaydevice 100 shown in this structure example is a top emission displaydevice, a light-transmitting material is used for the second electrode152. A reflective material is preferably used for the first electrode143. The EL layer 151 contains at least a light-emitting organiccompound. When voltage is applied between the first electrode 143 andthe second electrode 152 with the EL layer 151 interposed therebetweenso that current flows in the EL layer 151, the light-emitting element114 can emit light.

The first substrate 121 is provided to face the second substrate 101.The second substrate 101 and the first substrate 121 are bonded to eachother with the sealing layer 153 and the sealant 154 that is providedoutside the display portion 102 and on the inner side of the crackinhibiting region 110. Note that the sealant 154 is not necessarilyprovided and the first substrate 121 may be bonded only with the sealinglayer 153.

The buffer layer 120 is provided on the surface of the first substrate121, which faces the light-emitting element 114, with the bonding layer125 interposed therebetween. A color filter 127 and a black matrix 126are provided on the buffer layer 120 so as to overlap with thelight-emitting element 114 and the insulating layer 144, respectively.

On the other surface of the first substrate 121, which does not face thelight-emitting element 114, a transparent conductive film may beprovided to form a touch sensor, or a flexible substrate having afunction of a touch sensor may be attached.

[Material and Formation Method]

Materials and manufacturing methods of the aforementioned componentswill be described below.

[Flexible Substrate]

As the flexible substrate, an organic resin substrate, a glass substratethin enough to have flexibility, or the like can be used.

Examples of the materials include polyester resins such as polyethyleneterephthalate (PET) and polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, and a polyvinyl chloride resin. It is particularlypreferable to use a material with a low thermal expansion coefficient,for example, a material with a thermal expansion coefficient lower thanor equal to 30×10⁻⁶/K, such as a polyamide imide resin, a polyimideresin, or PET. It is also possible to use a substrate in which a fibrousbody is impregnated with a resin (also referred to as prepreg) or asubstrate whose thermal expansion coefficient is reduced by mixing aninorganic filler with an organic resin.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile modulus of elasticity or a fiber with a highYoung's modulus. Typical examples include a polyvinyl alcohol-basedfiber, a polyester-based fiber, a polyamide-based fiber, apolyethylene-based fiber, an aramid-based fiber, a polyparaphenylenebenzobisoxazole fiber, a glass fiber, and a carbon fiber. As the glassfiber, glass fiber using E glass, S glass, D glass, Q glass, or the likecan be used. These fibers may be used in a state of a woven fabric or anonwoven fabric, and a structure body in which this fibrous body isimpregnated with a resin and the resin is cured may be used as aflexible substrate. The structure body including the fibrous body andthe resin is preferably used as a flexible substrate, in which case thereliability against bending and damage due to local pressure can beincreased.

A material capable of transmitting light emitted from the EL layer 151is used for the flexible substrate through which light emitted from thelight-emitting element 114 is transmitted. To improve the outcouplingefficiency of the material provided on the light extraction side, therefractive index of the flexible, light-transmitting material ispreferably high. For example, a substrate obtained by dispersing aninorganic filler having a high refractive index into an organic resincan have a higher refractive index than the substrate formed of only theorganic resin. In particular, an inorganic filler having a particlediameter as small as 40 nm or less is preferably used, in which casesuch a filler can maintain optical transparency.

The substrate provided on the side opposite to the side through whichlight is transmitted does not need to have a light-transmittingproperty; therefore, a metal substrate, an alloy substrate, or the likecan be used as well as the above substrates. To obtain flexibility andbendability, the thickness of a substrate is preferably greater than orequal to 10 μm and less than or equal to 200 μm, more preferably greaterthan or equal to 20 μm and less than or equal to 50 μm. Although thereis no particular limitation on a material of the substrate, it ispreferable to use, for example, aluminum, copper, nickel, or a metalalloy such as an aluminum alloy or stainless steel. A conductivesubstrate containing a metal or an alloy material is preferably used asthe flexible substrate provided on the side through which light is nottransmitted, in which case the dissipation of heat generated from thelight-emitting element 114 can be improved.

In the case where a conductive substrate is used, a surface of thesubstrate is preferably oxidized or provided with an insulating film soas to be insulated. For example, an insulating film may be formed overthe surface of the conductive substrate by an electrodeposition method,a coating method such as a spin-coating method or a dip method, aprinting method such as a screen printing method, or a deposition methodsuch as an evaporation method or a sputtering method. Alternatively, thesurface of the substrate may be oxidized by being exposed to an oxygenatmosphere or heated in an oxygen atmosphere or by an anodic oxidationmethod.

In the case where the flexible substrate has an uneven surface, aplanarization layer may be provided to cover the uneven surface so thata flat insulating surface is formed. An insulating material can be usedfor the planarization layer; an organic material or an inorganicmaterial can be used. The planarization layer can be formed by adeposition method such as a sputtering method, a coating method such asa spin-coating method or a dip method, a discharging method such as anink jet method or a dispensing method, a printing method such as ascreen printing method, or the like.

As the flexible substrate, a material including a plurality of stackedlayers can also be used. For example, a material in which two or morekinds of layers formed of an organic resin are stacked, a material inwhich a layer formed of an organic resin and a layer formed of aninorganic material are stacked, or a material in which two or more kindsof layers formed of an inorganic material are stacked is used. With alayer formed of an inorganic material, moisture and the like areprevented from entering the inside, resulting in improved reliability ofthe display device.

As the inorganic material, an oxide material, a nitride material, or anoxynitride material of a metal or a semiconductor, or the like can beused. For example, silicon oxide, silicon nitride, silicon oxynitride,aluminum oxide, aluminum nitride, or aluminum oxynitride may be used.Note that in this specification, the nitride oxide refers to a materialcontaining a larger amount of nitrogen than oxygen, and the oxynitriderefers to a material containing a larger amount of oxygen than nitrogen.Note that the content of each element can be measured by, for example,Rutherford backscattering spectrometry (RBS).

For example, in the case where a layer formed of an organic resin and alayer formed of an inorganic material are stacked, the layer formed ofan inorganic material can be formed over or under the layer formed of anorganic resin by a sputtering method, a chemical vapor deposition (CVD)method, a coating method, or the like.

As the flexible substrate, a glass substrate thin enough to haveflexibility may also be used. Specifically, it is preferable to use asheet in which an organic resin layer, a bonding layer, and a glasslayer are sequentially stacked from the side close to the light-emittingelement 114. The thickness of the glass layer is greater than or equalto 20 μm and less than or equal to 200 μm, preferably greater than orequal to 25 μm and less than or equal to 100 μm. Such a thickness allowsthe glass layer to have both high flexibility and a high barrierproperty against water and oxygen. The thickness of the organic resinlayer is greater than or equal to 10 μm and less than or equal to 200μm, preferably greater than or equal to 20 μm and less than or equal to50 μm. With such an organic resin layer in contact with the glass layer,breakage or a crack of the glass layer can be inhibited, resulting inincreased mechanical strength. Forming the flexible substrate by usingsuch a composite material of a glass material and an organic resin makesit possible to obtain a flexible display device with extremely highreliability.

Alternatively, a substrate which does not have flexibility, such as aglass substrate, may be used.

[Light-Emitting Element]

As the light-emitting element, a self-luminous element can be used, andan element whose luminance is controlled by current or voltage isincluded in the category of the light-emitting element. For example, alight-emitting diode (LED), an organic EL element, or an inorganic ELelement can be used.

The light-emitting element 114 included in the display device 100 ofthis embodiment includes a pair of electrodes (the first electrode 143and the second electrode 152), and the EL layer 151 between the pair ofelectrodes. One of the pair of electrodes functions as an anode and theother functions as a cathode.

In the light-emitting element 114, a material transmitting light emittedfrom the EL layer 151 is used for the electrode on the light emissionside.

As the light-transmitting material, indium oxide, indium oxide-tinoxide, indium oxide-zinc oxide, zinc oxide, and zinc oxide to whichgallium is added can be used. Graphene may also be used. Other examplesare a metal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, andtitanium; and an alloy material containing any of these metal materials.A nitride of the metal material (e.g., titanium nitride) or the like mayalso be used. In the case of using the metal material (or the nitridethereof), the thickness is set small enough to be able to transmitlight. Alternatively, a stack including any of the above materials canalso be used as the conductive layer. For example, a layered film of asilver-magnesium alloy and indium oxide-tin oxide is preferably used, inwhich case electrical conductivity can be increased.

Such an electrode is formed by an evaporation method, a sputteringmethod, or the like. A discharging method such as an ink jet method, aprinting method such as a screen printing method, or a plating methodmay also be used.

Note that when the above conductive oxide having a light-transmittingproperty is formed by a sputtering method, the deposition under anatmosphere containing argon and oxygen increases the light-transmittingproperty.

Further, in the case where the conductive oxide film is formed over theEL layer, the conductive oxide film is preferably a layered film of afirst conductive oxide film formed under an argon-containing atmospherewith a reduced oxygen concentration and a second conductive oxide filmformed under an atmosphere containing argon and oxygen, in which casedeposition damage to the EL layer can be reduced. Here, the purity of anargon gas used for formation of the first conductive oxide film ispreferably high, and for example, it is preferable to use the argon gaswhose dew point is lower than or equal to −70° C., more preferably lowerthan or equal to −100° C.

A material capable of reflecting light emitted from the EL layer 151 ispreferably used for the electrode provided on the side opposite to theside through which light is transmitted.

As the light-reflecting material, for example, a metal such as aluminum,gold, platinum, silver, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, or palladium or an alloy containing any of these metalscan be used. Alternatively, lanthanum, neodymium, germanium, or the likemay be added to a metal or an alloy containing any of these metalmaterials. In addition, any of the following can be used: alloyscontaining aluminum (aluminum alloys) such as an aluminum-titaniumalloy, an aluminum-nickel alloy, and an aluminum-neodymium alloy; andalloys containing silver such as a silver-copper alloy, asilver-palladium-copper alloy, and a silver-magnesium alloy. Thesilver-copper alloy is preferable because of its high heat resistance.Furthermore, by stacking a metal film or a metal oxide film in contactwith an aluminum alloy film, oxidation of the aluminum alloy film can besuppressed. Examples of a material for the metal film or the metal oxidefilm are titanium and titanium oxide. Further alternatively, a filmcontaining any of the above light-transmitting materials and a filmcontaining any of the above metal materials may be stacked. For example,a layered film including silver and indium oxide-tin oxide, or a layeredfilm including a silver-magnesium alloy and indium oxide-tin oxide canbe used.

Such an electrode is formed by an evaporation method, a sputteringmethod, or the like. A discharging method such as an ink jet method, aprinting method such as a screen printing method, or a plating methodmay also be used.

The EL layer 151 includes at least a layer containing a light-emittingorganic compound (hereinafter also referred to as a light-emittinglayer), and may be either a single layer or a plurality of stackedlayers. As an example of the structure including a plurality of stackedlayers, a hole-injection layer, a hole-transport layer, a light-emittinglayer, an electron-transport layer, and an electron-injection layer canbe stacked in this order from an anode side. Note that not all of theselayers except the light-emitting layer are necessarily provided in theEL layer 151. Furthermore, each of these layers may be provided induplicate or more. Specifically, in the EL layer 151, a plurality oflight-emitting layers may be provided or another hole-injection layermay be provided over the electron-injection layer. Furthermore, anothercomponent such as a charge-generation layer or an electron-relay layermay be added as appropriate as an intermediate layer. Alternatively, aplurality of light-emitting layers exhibiting different colors may bestacked. For example, a white emission can be obtained by stacking twoor more layers emitting light of complementary colors.

The EL layer 151 can be formed by a vacuum evaporation method, adischarging method such as an ink jet method or a dispensing method, ora coating method such as a spin-coating method.

[Sealant, Sealing Layer, and Bonding Layer]

As the sealant 154 and the sealing layer 153, it is possible to use, forexample, a gel or a curable material such as a two-component-mixturetype resin, a thermosetting resin, or a light curable resin. Forexample, an epoxy resin, an acrylic resin, a silicone resin, a phenolresin, polyimide, polyvinyl chloride (PVC), polyvinyl butyral (PVB), orethylene vinyl acetate (EVA) can be used. In particular, a material withlow moisture permeability, such as an epoxy resin, is preferable.

A drying agent may be contained in the sealant 154 and/or the sealinglayer 153. For example, a substance that adsorbs moisture by chemicaladsorption, such as oxide of an alkaline earth metal (e.g., calciumoxide or barium oxide), can be used. Alternatively, a substance thatadsorbs moisture by physical adsorption, such as zeolite or silica gel,may be used as the drying agent. In the case where a granular dryingagent is used, light emitted from the light-emitting element 114 isdiffusely reflected by the drying agent; thus, a highly reliablelight-emitting device (particularly useful for lighting and the like)with improved viewing angle dependence can be achieved. Note that as thebonding layers 125 and 131, the same material as the sealant 154 may beused.

[Transistor]

There is no particular limitation on the structures of transistors inthe display portion 102, the signal line driver circuit 103, and thescan line driver circuit 104. For example, a forward staggeredtransistor or an inverted staggered transistor may be used. Furthermore,either a top-gate transistor or a bottom-gate transistor may be used. Inaddition, either a channel-etched transistor or a channel protectivetransistor may be used. In the case of a channel protective transistor,a channel protective film may be provided only over a channel region.Alternatively, an opening may be formed only in a portion where a sourceelectrode and a drain electrode are in contact with a semiconductorlayer and a channel protective film may be provided in an area otherthan the opening.

As a semiconductor applicable to a semiconductor layer in which achannel of a transistor is formed, for example, a semiconductor materialsuch as silicon or germanium, a compound semiconductor material, anorganic semiconductor material, or an oxide semiconductor material maybe used.

There is no particular limitation on the crystallinity of asemiconductor used for the transistors, and an amorphous semiconductoror a semiconductor having crystallinity (a microcrystallinesemiconductor, a polycrystalline semiconductor, a single crystalsemiconductor, or a semiconductor partly including crystal regions) maybe used. A semiconductor having crystallinity is preferably used, inwhich case deterioration of transistor characteristics can be reduced.

In the case where, for example, silicon is used as the semiconductor,amorphous silicon, microcrystalline silicon, polycrystalline silicon,single crystal silicon, or the like can be used.

In the case where an oxide semiconductor is used as the semiconductor,an oxide semiconductor containing at least one of indium, gallium, andzinc is preferably used. Typically, an In—Ga—Zn-based metal oxide can beused. An oxide semiconductor having a wider band gap and a lower carrierdensity than silicon is preferably used, in which case off-state leakagecurrent can be reduced.

In this structure example, a bottom-gate transistor is used; the case ofusing a top-gate transistor will be described in a later embodiment.

[Buffer Layer and Insulating Layer]

The buffer layer 120 has a function of inhibiting diffusion ofimpurities, particularly moisture, which have passed through the firstsubstrate 121 and the bonding layer 125. The second buffer layer 132 hasa function of inhibiting diffusion of impurities that have passedthrough the second substrate 101 and the bonding layer 131. Theinsulating layer 134 in contact with the semiconductor layer of thetransistor and the insulating layer 141 covering the transistorpreferably prevent impurities from diffusing into the semiconductorlayer. These layers can be formed using, for example, oxide or nitrideof a semiconductor such as silicon or oxide or nitride of a metal suchas aluminum. Alternatively, a layered film of such an inorganicinsulating material or a layered film of such an inorganic insulatingmaterial and an organic insulating material may be used.

As the inorganic insulating material, for example, a single layer of ora stack including one or more materials selected from aluminum nitride,aluminum oxide, aluminum nitride oxide, aluminum oxynitride, magnesiumoxide, gallium oxide, silicon nitride, silicon oxide, silicon nitrideoxide, silicon oxynitride, germanium oxide, zirconium oxide, lanthanumoxide, neodymium oxide, and tantalum oxide.

As the inorganic insulating material, a high-k material such as hafniumsilicate (HfSiO_(x)), hafnium silicate to which nitrogen is added(HfSi_(x)O_(y)N_(z)), hafnium aluminate to which nitrogen is added(HfAl_(x)O_(y)N_(z)), hafnium oxide, or yttrium oxide may be used.

The insulating layer 142 functions as a planarization layer coveringsteps formed due to a transistor, a wiring, or the like. For theinsulating layer 142, for example, an organic resin such as polyimide,acrylic, polyamide, or epoxy or an inorganic insulating material can beused. It is preferable to use a photosensitive resin (e.g., acrylic orpolyimide) for the insulating layer 142. The insulating layer 144 can beformed using the same material as the insulating layer 142.

[Crack Inhibiting Layer and Marker]

The crack inhibiting layer 122 and the marker 124 can be formed using aconductive material; furthermore, they are preferably formed using thesame material to simplify the process.

The crack inhibiting layer 122 is preferably formed of a conductivematerial that is highly resistant to external stress so as to hinder thedevelopment of a crack in the buffer layer 120 in contact with the crackinhibiting layer 122.

The marker 124 is used to mark the position to be cut in the case where,for example, a plurality of display devices 100 are manufactured at atime over a large substrate and divided into each, i.e., by a multiplepanel method. Hence, the marker 124 is preferably formed of a conductivematerial because in the case where the substrate is divided by a cuttingapparatus, a clear edge of a pattern reduces the misalignment of aposition to be read in the cutting apparatus.

Each of the clack inhibiting layer 122 and the marker 124 can be formedto have a single-layer structure or a layered structure using any ofmetal materials such as molybdenum, titanium, chromium, tantalum,tungsten, aluminum, copper, neodymium, and scandium, and an alloymaterial containing any of these elements. Alternatively, the clackinhibiting layer 122 and the marker 124 may each be formed using aconductive metal oxide.

The crack inhibiting layer 122 needs to have a thickness that allows themechanical strength to be maintained. Specifically, the crack inhibitinglayer 122 is formed as a conductive layer with a thickness of 50 nm to1000 nm, preferably 100 nm to 500 nm.

In addition, the crack inhibiting layer 122 needs to have a width thatallows the development of a crack to be hindered. However, an increasein the width of the crack inhibiting layer 122 might reduce the numberof display devices that can be obtained from a substrate in the casewhere the display device 100 is manufactured by a multiple panel methodor the like. Specifically, the crack inhibiting layer 122 is formed as aconductive layer with a width of 20 μm to 1000 μm, preferably 50 μm to500 μm.

[Connector]

For the connector 156, it is possible to use a paste-like or sheet-likematerial that is obtained by mixing metal particles into a thermosettingresin and for which anisotropic electric conductivity is provided bythermocompression bonding. As the metal particles, particles in whichtwo or more kinds of metals are layered, for example, nickel particlescoated with gold are preferably used.

[Color Filter and Black Matrix]

The color filter 127 is provided in order to adjust the color of lightemitted from the light-emitting element 114 to increase the colorpurity. For example, in a full-color display device using whitelight-emitting elements, a plurality of pixels provided with colorfilters of different colors are used. In that case, the color filtersmay be those of three colors of red (R), green (G), and blue (B) or fourcolors (yellow (Y) in addition to these three colors). Furthermore, awhite (W) pixel may be added to R, G, and B pixels (and a Y pixel), thatis, pixels of four colors (or five colors) may be used.

The black matrix 126 is provided between the adjacent color filters 127.The black matrix 126 shields a pixel from light emitted from thelight-emitting element 114 in an adjacent pixel, thereby preventingcolor mixture between the adjacent pixels. When the color filter 127 isprovided so that its end portion overlaps with the black matrix 126,light leakage can be reduced. The black matrix 126 can be formed using amaterial that blocks light emitted from the light-emitting element 114,for example, a metal material or an organic resin containing a pigment.Note that the black matrix 126 may be provided in a region other thanthe display portion 102, for example, in the signal line driver circuit103.

An overcoat may be formed to cover the color filter 127 and the blackmatrix 126. The overcoat protects the color filter 127 and the blackmatrix 126 and suppresses the diffusion of impurities included in thecolor filter 127 and the black matrix 126. The overcoat is formed usinga material that transmits light emitted from the light-emitting element114, and can be formed using an inorganic insulating film or an organicinsulating film.

Although this structure example shows the top emission display device,the display device may have a bottom emission structure. In that case,the color filter 127 is provided closer to the second substrate 101 thanthe light-emitting element 114 is. For example, the color filter may beprovided over the insulating layer 141. The black matrix 126 may beprovided to overlap with the transistor and the like.

Described in this structure example is a structure provided with a colorfilter, but a structure without a color filter may be employed, in whichcase each pixel includes any one of light-emitting elements exhibitinglight of different colors (e.g., R, G, and B).

The above is the description of the components.

[Example of Manufacturing Method]

An example of a method for manufacturing the display device 100 will bedescribed below with reference to drawings.

FIGS. 3A to 3C, FIGS. 4A and 4B, FIGS. 5A and 5B, and FIGS. 6A and 6Bare schematic cross-sectional views each illustrating a stage in themethod for manufacturing the display device 100 described below. FIGS.3A to 3C, FIGS. 4A and 4B, FIGS. 5A and 5B, and FIGS. 6A and 6Billustrate cross-sectional structures of the components in FIGS. 1A and1B.

[Formation of Separation Layer]

First, a separation layer 162 is formed over a support substrate 161.

A substrate having resistance high enough to withstand at least heat ina later step is used as the support substrate 161. Examples of thesupport substrate 161 include a glass substrate, a resin substrate, asemiconductor substrate, a metal substrate, and a ceramic substrate.

Note that it is preferable to use a large glass substrate as the supportsubstrate 161 to increase productivity. For example, a glass substratehaving any of the following sizes or a larger size can be used: the 3rdgeneration (550 mm×650 mm), the 3.5th generation (600 mm×720 mm or 620mm×750 mm), the 4th generation (680 mm×880 mm or 730 mm×920 mm), the 5thgeneration (1100 mm×1300 mm), the 6th generation (1500 mm×1850 mm), the7th generation (1870 mm×2200 mm), the 8th generation (2200 mm×2400 mm),the 9th generation (2400 mm×2800 mm or 2450 mm×3050 mm), and the 10thgeneration (2950 mm×3400 mm).

A high-melting-point metal material such as tungsten, titanium, ormolybdenum can be used for the separation layer 162. Tungsten ispreferably used.

The separation layer 162 can be formed by, for example, a sputteringmethod.

[Formation of Buffer Layer]

Then, the buffer layer 120 is formed over the separation layer 162 (FIG.3A).

For the buffer layer 120, an inorganic insulating material such assilicon oxide, silicon oxynitride, silicon nitride oxide, siliconnitride, or aluminum oxide can be used. The buffer layer 120 can be asingle layer or stacked layers containing any of these inorganicinsulating materials.

The buffer layer 120 serves as a barrier film preventing entry ofimpurities from the outside of the support substrate 161. The bufferlayer 120 also has a function of releasing hydrogen to the separationlayer 162 by heating as described later. Therefore, it is particularlypreferable that the buffer layer 120 include two or more stacked layers,at least one of which releases hydrogen when heated, and another ofwhich, a layer further from the separation layer 162 than the layerreleasing hydrogen is, does not transmit impurities. For example, thebuffer layer 120 has a structure in which a layer containing siliconoxynitride and a layer containing silicon nitride are stacked in thisorder from the separation layer 162.

The buffer layer 120 can be formed by a film formation method such as asputtering method or a plasma CVD method. In particular, the bufferlayer 120 is preferably formed by a plasma CVD method using a depositiongas containing hydrogen.

A surface of the separation layer 162 is oxidized when the buffer layer120 is formed, and as a result, an oxide (not shown) is formed betweenthe separation layer 162 and the buffer layer 120. The oxide is a layercontaining an oxide of the metal included in the separation layer 162.The oxide layer preferably contains tungsten oxide.

Tungsten oxide is generally represented by WO_((3-x)) and is anon-stoichiometric compound which can have a variety of compositions,typically WO₃, W₂O₅, W₄O₁₁, and WO₂. Titanium oxide TiO_((2-x)) andmolybdenum oxide MoO_((3-x)) are also non-stoichiometric compounds.

The oxide layer at this stage preferably contains a large amount ofoxygen. For example, in the case where tungsten is used for theseparation layer 162, the oxide layer is preferably a tungsten oxidelayer containing WO₃ as its main component.

The oxide layer can also be formed over the surface of separation layer162 in advance by performing plasma treatment on the surface of theseparation layer 162 in an atmosphere containing an oxidized gas(preferably a dinitrogen monoxide gas) before the formation of thebuffer layer 120. When such a method is employed, the thickness of theoxide layer can vary depending on the conditions for the plasmatreatment, and the thickness of the oxide layer can be controlled moreeffectively than in the case where plasma treatment is not performed.

The thickness of the oxide layer is, for example, greater than or equalto 0.1 nm and less than or equal to 100 nm, preferably greater than orequal to 0.5 nm and less than or equal to 20 nm. Note that the oxidelayer with an extremely small thickness cannot be observed in across-sectional image in some cases.

[Heat Treatment]

Next, heat treatment is performed to change the quality of the oxidelayer. By the heat treatment, hydrogen is released from the buffer layer120 to the oxide layer.

The metal oxide in the oxide layer is reduced by hydrogen supplied tothe oxide layer, so that a plurality of regions with differentproportions of oxygen are mixed in the oxide layer. For example, in thecase where tungsten is used for the separation layer 162, WO₃ in theoxide layer is reduced to generate an oxide with a proportion of oxygenlower than that of WO₃ (e.g., WO₂), resulting in a state where WO₃ andthe oxide with the lower proportion of oxygen are mixed. The crystalstructure of such a metal oxide depends on the proportion of oxygen;thus, when a plurality of regions with different proportions of oxygenare provided in the oxide layer, the mechanical strength of the oxidelayer is reduced. As a result, the oxide layer is likely to be damagedinside, which facilitates a later separation step.

The heat treatment may be performed at a temperature higher than orequal to the temperature at which hydrogen is released from the bufferlayer 120 and lower than or equal to the temperature at which thesupport substrate 161 is softened. Furthermore, the heat treatment ispreferably performed at a temperature higher than or equal to thetemperature at which a reduction reaction between hydrogen and the metaloxide in the oxide layer occurs. For example, in the case where tungstenis used for the separation layer 162, the heating temperature is higherthan or equal to 420° C., higher than or equal to 450° C., higher thanor equal to 600° C., or higher than or equal to 650° C.

As the temperature of the heat treatment increases, a larger amount ofhydrogen can be released from the buffer layer 120, which facilitates alater separation step.

However, even when the heating temperature is reduced in considerationof the heat resistance of the support substrate 161 and theproductivity, separation can be performed effectively by performingplasma treatment on the separation layer 162 to form the oxide layer inadvance as described above.

[Formation of Crack Inhibiting Layer and Marker]

After that, a conductive film is formed over the buffer layer 120. Aresist mask is then formed over the conductive film by aphotolithography method or the like, and unnecessary portions of theconductive film are etched. Then, the resist mask is removed, so thatthe marker 124 and the crack inhibiting region 110 including a pluralityof crack inhibiting layers 122 are formed (FIG. 3B).

Note that the aforementioned heat treatment may be performed after theformation of the crack inhibiting layers 122 and the marker 124. Such aprocess prevents the conductive film over the buffer layer 120 frombeing lifted after the formation.

When the heat treatment is performed on exposed surfaces of the crackinhibiting layers 122 and the marker 124, the surfaces are damaged byoxidation or the like in some cases. Therefore, part of the buffer layer120 may be formed over the crack inhibiting layers 122 and the marker124 (see FIG. 21). In FIG. 21, films included in a stack of a bufferlayer 120 a and a buffer layer 120 b are preferably the same as thefilms included in the buffer layer 120. With such a structure, damage tothe surfaces of the crack inhibiting layers 122 and the marker 124 canbe inhibited without changing the transmittance of the entire bufferlayer.

For example, the buffer layer 120 a is a stack of a silicon oxynitridefilm with a thickness of approximately 600 nm, a silicon nitride filmwith a thickness of approximately 200 nm, a silicon oxynitride film witha thickness of approximately 200 nm, and a silicon nitride oxide filmwith a thickness of approximately 140 nm; and the buffer layer 120 b isa silicon oxynitride film with a thickness of approximately 100 nm.

Alternatively, the buffer layer 120 a is a stack of a silicon oxynitridefilm with a thickness of approximately 600 nm, a silicon nitride filmwith a thickness of approximately 280 nm, a silicon oxynitride film witha thickness of approximately 180 nm, a silicon nitride oxide film with athickness of approximately 140 nm, and a silicon oxynitride film with athickness of approximately 115 nm; and the buffer layer 120 b is asilicon oxynitride film with a thickness of approximately 100 nm.

[Formation of Black Matrix and Color Filter]

Subsequently, the black matrix 126 and the color filter 127 are formedover the buffer layer 120 (FIG. 3C). The black matrix 126 and the colorfilter 127 are formed by a printing method, an ink jet method, aphotolithography method, or the like.

[Formation of Gate Electrode]

Next, a support substrate 163 provided with the separation layer 164 andthe second buffer layer 132 is prepared. The separation layer 164 andthe second buffer layer 132 are formed in a manner similar to that ofthe separation layer 162 and the buffer layer 120.

After that, a conductive film is formed over the second buffer layer132. A resist mask is then formed over the conductive film by aphotolithography method or the like, and unnecessary portions of theconductive film are etched. Then, the resist mask is removed, so thatthe gate electrode 133 is formed.

At this time, wirings and the like which form a circuit may be formedsimultaneously.

The conductive film to be the gate electrode 133 is formed by asputtering method, an evaporation method, a CVD method, or the like.

[Formation of Gate Insulating Layer]

Then, the insulating layer 134 is formed to cover the gate electrode133.

The insulating layer 134 can be formed by a plasma CVD method, asputtering method, or the like.

[Formation of Semiconductor Layer]

After that, a semiconductor film is formed over the insulating layer134. A resist mask is then formed over the semiconductor film by aphotolithography method or the like, and unnecessary portions of thesemiconductor film are etched. Then, the resist mask is removed, so thatthe semiconductor layer 135 included in a transistor is formed.

The semiconductor film is formed by an appropriate method depending on amaterial. For example, a sputtering method, a CVD method, an MBE method,an atomic layer deposition (ALD) method, or a pulsed laser deposition(PLD) method can be used.

An oxide semiconductor is preferably used as a semiconductor in thesemiconductor layer. In particular, an oxide semiconductor having awider band gap than silicon is preferably used. A semiconductor materialhaving a wider band gap and a lower carrier density than silicon ispreferably used because the off-state current of the transistor can bereduced.

The oxide semiconductor preferably contains, for example, at leastindium (In) or zinc (Zn). The oxide semiconductor further preferablycontains an In-M-Zn-based oxide (M is a metal such as Al, Ti, Ga, Ge, Y,Zr, Sn, La, Ce, or Hf).

As the semiconductor layer, it is particularly preferable to use anoxide semiconductor film including a plurality of crystal parts whosec-axes are aligned perpendicular to a surface on which the semiconductorlayer is formed or the top surface of the semiconductor layer and inwhich the adjacent crystal parts have no grain boundary.

There is no grain boundary in such an oxide semiconductor; therefore,generation of a crack in an oxide semiconductor film that is caused bystress when a display panel is bent is prevented. Such an oxidesemiconductor can thus be preferably used for a flexible display panelthat is used in a bent state, or the like.

In the case where polycrystalline silicon is used for the semiconductorfilm, a film of amorphous silicon is deposited and subjected tocrystallization (e.g., laser light irradiation or heat treatment) toform a semiconductor film including polycrystalline silicon.

[Source Electrode and Drain Electrode]

After that, a conductive film is formed over the insulating layer 134and the semiconductor layer 135. A resist mask is then formed over theconductive film by a photolithography method or the like, andunnecessary portions of the conductive film are etched. Then, the resistmask is removed, so that the electrodes 136 serving as a source and adrain electrode of the transistor are formed (FIG. 4A).

At this time, wirings and the like which form a circuit may be formedsimultaneously.

The conductive film is formed by a sputtering method, an evaporationmethod, a CVD method, or the like.

At this stage, the transistors 111, 112, and 113 are obtained.

[Formation of Insulating Layer]

Subsequently, the insulating layer 141 that covers the insulating layer134, the semiconductor layer 135, and the electrode 136 is formed. Atthis time, an opening reaching one of the electrodes 136 of the currentcontrol transistor 113 and a wiring to be the external connectionterminal 105 is formed in the insulating layer 141.

The insulating layer 141 can be formed by a plasma CVD method, asputtering method, or the like.

Note that this manufacturing method shows an example in which theinsulating layer 141 over the semiconductor layer 135 is a single layer,but the insulating layer 141 may include two or more stacked layers.

[Formation of Planarization Layer]

Then, the insulating layer 142 serving as a planarization layer isformed. At this time, an opening reaching one of the electrodes 136 ofthe current control transistor 113 and a wiring to be the externalconnection terminal 105 is formed in the insulating layer 142.

For example, the insulating layer 142 is preferably formed in such amanner that a photosensitive organic resin is applied by a spin coatingmethod or the like, and then is subjected to selective light exposureand development. As another formation method, a sputtering method, anevaporation method, a droplet discharging method (e.g., an inkjetmethod), a screen printing method, an offset printing method, or thelike may be used.

[Formation of First Electrode]

After that, a conductive film is formed over the insulating layer 142. Aresist mask is then formed over the conductive film by aphotolithography method or the like, and unnecessary portions of theconductive film are etched. Then, the resist mask is removed, so thatthe first electrode 143 electrically connected to one of the electrodes136 of the transistor 113 is formed.

At this time, wirings and the like which form a circuit may be formedsimultaneously. In this example of manufacturing method, a wiring isformed over the same conductive film as the electrode 136 in a portionserving as the external connection terminal, so that the externalconnection terminal 105 is formed.

The conductive film is formed by a sputtering method, an evaporationmethod, a CVD method, or the like.

[Formation of Insulating Layer]

Then, the insulating layer 144 is formed to cover an end portion of thefirst electrode 143. At this time, an opening reaching the wiringserving as the external connection terminal 105 is formed in theinsulating layer 144.

For example, the insulating layer 144 is preferably formed in such amanner that a photosensitive organic resin is applied by a spin coatingmethod or the like, and then is subjected to selective light exposureand development. As another formation method, a sputtering method, anevaporation method, a droplet discharging method (e.g., an inkjetmethod), a screen printing method, an offset printing method, or thelike may be used.

Note that an insulating layer may be provided over the insulating layer144. In FIGS. 1A and 1B, the insulating layer over the insulating layer144 in the display portion 102 adjusts the distance between the firstsubstrate 121 and the second substrate 101. The insulating layer can beformed using the same material as the insulating layer 144.

[Formation of Light-Emitting Element]

The EL layer 151 and the second electrode 152 are sequentially formedover the first electrode 143; thus the light-emitting element 114 isobtained (FIG. 4B).

The EL layer 151 can be formed by a vacuum evaporation method, adischarging method such as an ink jet method or a dispensing method, ora coating method such as a spin-coating method. The second electrode 152is formed by an evaporation method, a sputtering method, or the like.

[Bonding]

Then, over a surface of the support substrate 161 that is provided withthe color filter 127 and the like, or over a surface of the supportsubstrate 163 that is provided with the light-emitting element 114, thesealant 154 is formed to surround the display portion 102.

The sealant 154 is formed in such a manner that a curable resin isapplied by, for example, a discharging method such as a dispensingmethod or a printing method such as a screen printing method, and asolvent in the resin is vaporized.

Then, the sealing layer 153 is formed over the support substrate 161 orthe support substrate 163. The sealing layer 153 can be formed in amanner similar to that of the sealant 154.

The sealant 154 is provided so that the sealing with the sealing layer153 is performed better. The sealant 154 is not necessarily provided ifthe sealing is performed adequately by the sealing layer 153.

Subsequently, the support substrate 161 and the support substrate 163are bonded and the sealant 154 and the sealing layer 153 are cured,whereby the support substrate 161 and the support substrate 163 areattached to each other (FIG. 5A).

[Separation]

Then, the support substrate 161 is separated (FIG. 5B), and the exposedbuffer layer 120 is bonded to the first substrate 121 with the bondinglayer 125 therebetween. Furthermore, the support substrate 163 isseparated, and the exposed second buffer layer 132 is bonded to thesecond substrate 101 with the bonding layer 131 therebetween (FIG. 6A).FIG. 6A shows a structure in which the first substrate 121 overlaps withthe external connection terminal 105; however, the first substrate 121does not necessarily overlap with the external connection terminal 105.

For the separation, for example, the support substrate 163 is fixed to asuction stage and a separation starting point is formed between theseparation layer 162 and the buffer layer 120. The separation startingpoint may be formed by, for example, inserting a sharp instrument suchas a knife between the layers. Alternatively, the separation startingpoint may be formed by irradiating a region of the separation layer 162with laser light to melt, evaporate, or thermally break the region.Further alternatively, the separation starting point may be formed bydripping liquid (e.g., alcohol, water, or water containing carbondioxide) onto an end portion of the separation layer 162 so that theliquid penetrates into an interface between the separation layer 162 andthe buffer layer 120 by using capillary action.

Then, physical force is gently applied to the area where the separationstarting point is formed in a direction substantially perpendicular tothe bonded surfaces, so that separation can be performed without damageto the buffer layer 120 and layers provided thereover.

It is preferable that a separation starting point be formed in an endportion of the support substrate 161 so that the separation proceedsfrom the end portion. In the formation of the separation starting point,a crack occurs in some cases in the buffer layer 120 near the endportion of the support substrate 161. The crack formed at this timemight develop from the outer side to the inner side of the buffer layer120 as the separation proceeds. However, even when such a crack occurs,development of the crack can be stopped in a region where the crackinhibiting region 110 is provided because the display portion 102 issurrounded by the crack inhibiting region 110; thus, the crack can beeffectively prevented from reaching the display portion 102.

A method for separating the support substrate 163 will be describednext. For example, another support substrate is bonded to the firstsubstrate 121 with a removable bonding layer (e.g., a water-solubleadhesive or a low-viscosity adhesive) therebetween. Then, a separationstarting point may be formed between the separation layer 164 and thesecond buffer layer 132 while the other support substrate is fixedsimilarly to the above. Alternatively, the first substrate 121 is fixedto a suction pad while the support substrate 163 is fixed; then, aseparation starting point is formed between the separation layer 164 andthe second buffer layer 132. After that, the suction pad is gentlyraised up so that the first substrate 121 and the like are not bent.

Lastly, an opening is formed in the first substrate 121, the bondinglayer 125, the buffer layer 120, and the sealing layer 153, whereby theexternal connection terminal 105 is exposed (FIG. 6B). Note that in thecase where the first substrate 121 does not overlap with the externalconnection terminal 105, an opening is formed in the buffer layer 120and the sealing layer 153. There is no particular limitation on themethod for forming the opening; for example, a laser ablation method, anetching method, or an ion beam sputtering method can be employed. Asanother method, a cut may be made in a film over the external connectionterminal 105 with a sharp knife or the like and part of the film may beseparated by physical force. In that case, an opening can be formedwithout damage to the external connection terminal 105 when a film witha low adhesion to a conductive film such as an EL layer is provided overthe electrode 143, which is the outermost surface of the externalconnection terminal 105.

Through the above process, the display device 100 can be manufactured.

Note that any of a variety of methods can be used as appropriate for theaforementioned separation process. For example, when a layer including ametal oxide film is formed as the separation layer on the side incontact with the buffer layer, the metal oxide film is embrittled bycrystallization, whereby the buffer layer can be separated from thesupport substrate. Alternatively, when an amorphous silicon filmcontaining hydrogen is formed as the separation layer between a supportsubstrate having high heat resistance and a buffer layer, the amorphoussilicon film is removed by laser light irradiation or etching, wherebythe buffer layer can be separated from the support substrate.Alternatively, after a layer including a metal oxide film is formed asthe separation layer on the side in contact with the buffer layer, themetal oxide film is embrittled by crystallization, and part of theseparation layer is removed by etching using a solution or a fluoridegas such as NF₃, BrF₃, or ClF₃, whereby the separation can be performedat the embrittled metal oxide film. Further alternatively, the followingmethod may be employed: a film containing nitrogen, oxygen, hydrogen, orthe like (e.g., an amorphous silicon film containing hydrogen, an alloyfilm containing hydrogen, or an alloy film containing oxygen) is used asthe separation layer, and the separation layer is irradiated with laserlight to release the nitrogen, oxygen, or hydrogen contained in theseparation layer as gas, thereby promoting separation between the bufferlayer and the support substrate. Alternatively, it is possible to use amethod in which the support substrate provided with the buffer layer isremoved mechanically or by etching using a solution or a fluoride gassuch as NF₃, BrF₃, or ClF₃. In this case, the separation layer is notnecessarily provided.

When a plurality of the above-described separation methods are combined,the separation process can be conducted easily. In other words,separation can be performed with physical force (by a machine or thelike) after performing laser light irradiation, etching on theseparation layer with a gas, a solution, or the like, or mechanicalremoval with a sharp knife, scalpel or the like so that the separationlayer and the buffer layer can be easily separated from each other.

Separation of the buffer layer from the support substrate may beperformed by soaking the interface between the separation layer and thebuffer layer in a liquid. Furthermore, the separation may be performedwhile a liquid such as water is being poured.

As another separation method, in the case where the separation layer isformed using tungsten, it is preferable that the separation be performedwhile etching the separation layer using a mixed solution of ammoniumwater and a hydrogen peroxide solution.

Note that the separation layer is not necessarily provided in the casewhere separation at the interface between the support substrate and thebuffer layer is possible.

For example, glass is used as the support substrate, an organic resinsuch as polyimide is formed in contact with the glass, and an insulatingfilm, a transistor, and the like are formed over the organic resin. Inthis case, heating the organic resin enables the separation at theinterface between the support substrate and the organic resin. FIG. 7 isa schematic cross-sectional view of the display device 100 manufacturedby separation at the interface between the support substrate and theorganic resin. An organic resin layer 128 is provided on the surface ofthe first substrate 121 that faces the light-emitting element 114, withthe bonding layer 125 therebetween, and an organic resin layer 138 isprovided over the second substrate 101 with the bonding layer 131therebetween. In addition, the crack inhibiting region 110 and themarker 124, and the buffer layer 120 are provided in this order incontact with the organic resin layer 128. The second buffer layer 132 isprovided over the organic resin layer 138. The other parts of thestructure are similar to those in FIG. 1B. With such a structure, evenwhen a crack is generated in an end portion of the buffer layer 120 asthe separation is caused at the interface between the support substrateand the organic resin, the crack can be prevented from developing acrossthe crack inhibiting region 110.

Alternatively, separation at the interface between a metal layer and theorganic resin may be performed in the following manner: the metal layeris provided between the support substrate and the organic resin andcurrent is made to flow in the metal layer so that the metal layer isheated.

Although this manufacturing method shows a process of fabricating theone display device 100, in terms of productivity, a plurality of displaydevices 100 are preferably manufactured at a time over a largesubstrate. In that case, the substrate is cut along the markers 124, forexample, after the bonding step or the separation step. FIG. 8 is aschematic top view of the four display devices 100 manufactured at atime over a large substrate. The substrate is cut along a dashed line toobtain each display device 100.

Through the above process, a display device with fewer defects caused bya crack can be provided.

MODIFICATION EXAMPLE OF DISPLAY DEVICE

Modification examples of the display device 100 will be described below.

Modification Example 1

FIG. 9 is a schematic cross-sectional view of the display device 100that includes a cover layer 123 in contact with the crack inhibitinglayer 122.

In the case where the marker 124 is not formed in the display device100, the crack inhibiting layer 122 is preferably formed using the samematerial as the black matrix 126 so as not to increase the number ofsteps.

To prevent a crack more effectively, the cover layer 123 may be formedto cover a plurality of crack inhibiting layers 122. The development ofthe crack can be hindered when stress is distributed unevenly in thedirection where the crack develops at the interface between the bufferlayer 120 and each of the crack inhibiting layers 122 and the coverlayer 123. Therefore, the cover layer 123 is preferably formed using amaterial different from that of the crack inhibiting layers 122. Thecover layer 123 can be formed of a conductive material or a resinmaterial.

In the display device 100 illustrated in FIG. 9, the crack inhibitinglayers 122 are formed using the same material as the black matrix 126and the cover layer 123 is formed using the same material as the colorfilter 127.

Note that in FIG. 9, an insulating layer 145 is formed over theinsulating layer 144 in the display portion 102. The insulating layer145 adjusts the distance between the first substrate 121 and the secondsubstrate 101. The insulating layer 145 can be formed using the samematerial as the insulating layer 144.

Modification Example 2

FIG. 10 is a schematic cross-sectional view of the display device 100that includes a second crack inhibiting region 115 over the buffer layer132.

In the display device 100 illustrated in FIG. 10, the second crackinhibiting region 115 including a plurality of second crack inhibitinglayers 137 is provided to overlap with the crack inhibiting region 110.When the second crack inhibiting region 115 is provided to surround notonly the display portion 102 but also the signal line driver circuit103, the scan line driver circuit 104, the external connection terminal105, and the like, a crack generated from an end portion of the secondbuffer layer 132 can be prevented from reaching these portions,inhibiting failure such as the malfunction of the display device 100.

Note that the second crack inhibiting layer 137 is preferably formed incontact with the second buffer layer 132 with use of a conductivematerial or a resin material similarly to the crack inhibiting layer122. In the display device 100 illustrated in FIG. 10, the second crackinhibiting layer 137 is formed using the same material as the gateelectrode 133. The second crack inhibiting layer 137 is thus preferablyformed using the same material as the electrode or wiring included inthe transistors (111, 112, and 113) or the light-emitting element 114 soas not to increase the number of steps.

Modification Example 3

FIG. 11A is a schematic top view of the display device 100 in which thecrack inhibiting region 110 is provided closer to the display portion102 than the external connection terminal 105 is. FIG. 11B is aschematic cross-sectional view along lines A2-B2, C2-D2, and E2-F2 inFIG. 11A.

In the aforementioned manufacturing method, the crack inhibiting region110 is provided outside the external connection terminal 105. Incontrast, the crack inhibiting region 110 is provided inside theexternal connection terminal 105 in FIGS. 11A and 11B. When an openingis formed in the buffer layer 120 and the sealing layer 153 in a regionoverlapping with the external connection terminal 105 in theaforementioned manufacturing method, a crack might occur in an endportion of the opening in the buffer layer 120. In that case, thestructure in FIGS. 11A and 11B prevents the crack from developing intothe display portion 102.

In addition, the outer size of the display device 100 can be reducedwhen the crack inhibiting region 110 is provided inside the externalconnection terminal 105 as compared to the case where it is providedoutside. This increases the number of display devices 100 that can beobtained at a time from one large substrate by a multiple panel methodor the like.

Note that the display device including the light-emitting element isdescribed in this embodiment as an example; however, one embodiment ofthe present invention is not limited to this example. A variety ofsemiconductor devices and a variety of display devices can be given asexamples of devices in which flexible substrates that are a feature ofone embodiment of the present invention can be used. For example,flexible substrates that are a feature of one embodiment of the presentinvention can be used as substrates in the following elements ordevices. Examples include an EL element (e.g., an EL element includingorganic and inorganic materials, an organic EL element, or an inorganicEL element), an LED (e.g., a white LED, a red LED, a green LED, or ablue LED), a transistor (a transistor which emits light depending oncurrent), an electron emitter, a liquid crystal element, electronic ink,an electrophoretic element, a grating light valve (GLV), a plasmadisplay panel (PDP), a micro electro mechanical system (MEMS), a digitalmicromirror device (DMD), a digital micro shutter (DMS), aninterferometric modulator display (IMOD), a MEMS shutter displayelement, an optical interference type MEMS display element, anelectrowetting element, a piezoelectric ceramic display, or a carbonnanotube, which are display media whose contrast, luminance,reflectivity, transmittance, or the like is changed by electromagneticaction. Examples further include a display device having electronemitters, such as a field emission display (FED) or an SED-type flatpanel display (SED: surface-conduction electron-emitter display).Examples further include a display device having a liquid crystalelement, such as a liquid crystal display (e.g., a transmissive liquidcrystal display, a transflective liquid crystal display, a reflectiveliquid crystal display, a direct-view liquid crystal display, or aprojection liquid crystal display). Examples further include a displaydevice including electronic ink, electronic liquid powder, orelectrophoretic elements, such as electronic paper. In the case of atransflective liquid crystal display or a reflective liquid crystaldisplay, some or all of pixel electrodes function as reflectiveelectrodes. For example, some or all of pixel electrodes are formed tocontain aluminum, silver, or the like. In such a case, a storage circuitsuch as an SRAM can be provided under the reflective electrodes, leadingto lower power consumption.

This embodiment can be implemented in an appropriate combination withthe other embodiments and example described in this specification.

Embodiment 2

Described in this embodiment is a light-emitting module in which a touchpanel having a function of a touch sensor is added to the display deviceshown in Embodiment 1. Note that the components similar to those inEmbodiment 1 will not be described below.

[Structure Example of Display Device]

FIG. 12 is a schematic cross-sectional view of a light-emitting module200.

A light-emitting module 200 includes the display device 100 and a touchsensor 201. The display device 100 includes the first substrate 121, thesecond substrate 101, and the display portion 102. The touch sensor 201is provided on a surface of a substrate 221 that faces the displaydevice 100, with a buffer layer 220 therebetween. Note that the firstsubstrate 121, the second substrate 101, and the substrate 221 are allpreferably flexible substrates.

A plurality of wirings 231 are electrically connected to the touchsensor 201. In addition, the plurality of wirings 231 are led to aperipheral portion of the substrate 221 and partly form a terminal. Theterminal is electrically connected to an FPC 256 via a connector 255.

In the touch sensor 201, a crack inhibiting region 210 is provided incontact with the buffer layer 220. The crack inhibiting region 210includes a plurality of crack inhibiting layers 222 formed using thesame material as the plurality of wirings 231. By providing the crackinhibiting region 210 in a peripheral portion of the touch sensor 201,in the case where, for example, the light-emitting module 200 is held ina high temperature and high humidity environment, a crack generated inan end portion of the buffer layer 220 can be prevented from developinginto the touch sensor 201.

As the touch sensor 201, a capacitive touch sensor can be used. Examplesof the capacitive touch sensor include a surface capacitive touch sensorand a projected capacitive touch sensor.

Examples of the projected capacitive touch sensor include aself-capacitive touch sensor and a mutual capacitive touch sensor, whichdiffer mainly in the driving method. The use of a mutual capacitivetouch sensor is preferable because multiple points can be sensedsimultaneously.

An example of using a projected capacitive touch sensor will bedescribed below.

Note that the configuration of the touch sensor is not limited to theabove, and a variety of sensors that can sense the closeness or thecontact of a sensing target such as a finger can be used.

The projected capacitive touch sensor 201 includes electrodes 234 andelectrodes 235. The electrodes 234 are electrically connected to any ofthe plurality of wirings 231, and the electrodes 235 are electricallyconnected to any of the other wirings 231.

A wiring 232 electrically connects the two electrodes 234 between whichone of the electrodes 235 is positioned. The intersecting area of theelectrode 235 and the wiring 232 is preferably as small as possible.Such a structure allows a reduction in the area of a region where theelectrodes are not provided, reducing unevenness in transmittance. As aresult, unevenness in the luminance of light transmitted through thetouch sensor 201 can be reduced.

Note that the electrodes 234 and 235 can have any of a variety ofshapes. For example, a structure may be employed in which the pluralityof electrodes 234 are arranged so that gaps between the electrodes 234are reduced as much as possible, and the plurality of electrodes 235 arespaced apart from the electrodes 234 with an insulating layer interposedtherebetween to have regions not overlapping with the electrodes 234. Inthis case, it is preferable to provide, between two adjacent electrodes235, a dummy electrode electrically insulated from these electrodesbecause the area of regions having different transmittances can bereduced.

In the touch sensor 201, a surface of the buffer layer 220 that facesthe display device 100 is provided with the wiring 232 electricallyconnecting the adjacent electrodes 234, an insulating layer 233, theelectrodes 234 and 235 provided in a staggered arrangement on theinsulating layer 233, and an insulating layer 236.

With a bonding layer 225, the insulating layer 236 is attached to thesurface of the first substrate 121 that does not face the light-emittingelement 114 so that the touch sensor 201 overlaps with the displayportion 102.

In this structure example, a top emission light-emitting module is usedas the display device 100. In the case where the display device 100 is abottom emission module, with the bonding layer 225, the insulating layer236 is attached to the surface of the second substrate 101 that does notface the light-emitting element 114.

The buffer layer 220 has a function of inhibiting diffusion ofimpurities, particularly moisture, which have passed through thesubstrate 221. The buffer layer 220 can be formed using, for example,oxide or nitride of a semiconductor such as silicon or oxide or nitrideof a metal such as aluminum. Alternatively, a layered film of such aninorganic insulating material or a layered film of such an inorganicinsulating material and an organic insulating material may be used.

The wiring 232 is preferably formed using a light-transmittingconductive material, in which case the aperture ratio of thelight-emitting module can be increased. As the light-transmittingconductive material, a conductive oxide such as indium oxide, indiumoxide-tin oxide, indium oxide-zinc oxide, zinc oxide, and zinc oxide towhich gallium is added, or graphene can be used.

The wiring 232 can be formed by depositing a light-transmittingconductive material on the buffer layer 220 by a sputtering method andthen removing unnecessary portions by any of various patterningtechniques such as a photolithography method. Graphene may be formed bya CVD method or by applying a solution in which graphene oxide isdispersed and then reducing the solution.

Examples of a material for the insulating layer 233 include a resin suchas acrylic or epoxy resin, a resin having a siloxane bond, and aninorganic insulating material such as silicon oxide, silicon oxynitride,or aluminum oxide.

Furthermore, an opening reaching the wiring 232 is formed in theinsulating layer 233, and the electrodes 234 and 235 are formed by amethod similar to the manufacturing method of the wiring 232.

Each of the electrodes 235 extends in one direction, and a plurality ofelectrodes 235 are provided in the form of stripes.

The wiring 232 intersects with one of the electrodes 235.

A pair of electrodes 234 are provided with one of the electrodes 235provided therebetween. The wiring 232 electrically connects the adjacentelectrodes 234.

Note that the plurality of electrodes 234 are not necessarily arrangedin the direction orthogonal to one of the electrodes 235 and may bearranged to intersect with the electrode 235 at an angle of less than 90degrees.

One of the wirings 231 is electrically connected to one of theelectrodes 234 or one of the electrodes 235. Part of the wirings 231serves as a terminal. For the wirings 231, a metal material such asaluminum, gold, platinum, silver, nickel, titanium, tungsten, chromium,molybdenum, iron, cobalt, copper, or palladium or an alloy materialcontaining any of these metal materials can be used.

Note that an insulating layer for protecting the touch sensor 201 may beprovided. In this structure example, the insulating layer 236 isprovided to cover the insulating layer 233, the electrode 234, and theelectrode 235.

Furthermore, a connector 255 electrically connects any of the wirings231 to the FPC 256.

As the connector 255, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

The bonding layer 225 has a light-transmitting property. For example, athermosetting resin or an ultraviolet curable resin can be used;specifically, a resin such as an acrylic resin, a urethane resin, anepoxy resin, or a resin having a siloxane bond can be used.

At least part of this embodiment can be implemented in an appropriatecombination with the other embodiments described in this specification.

Embodiment 3

Described in this embodiment is a display device having a structuredifferent from the structures shown in Embodiments 1 and 2. Note thatthe components similar to those in Embodiment 1 will not be describedbelow.

[Structure Example of Display Device]

A structure example of an image display device in which a liquid crystalelement is used as a display element will be described below.

FIG. 13A is a schematic top view of a display device 300. FIG. 13B is aschematic cross-sectional view along lines A3-B3, C3-D3, and E3-F3 inFIG. 13A. The display device 300 differs from the display device 100described in Embodiment 1 mainly in that a liquid crystal element isused as a display element, a transistor has a different structure, and acrack inhibiting region is arranged in a different area.

The display portion 102 includes a liquid crystal element 314 using anin-plane switching (IPS) mode. In the liquid crystal element 314, theorientation of a liquid crystal is controlled by an electric fieldgenerated in a direction parallel to the substrate surface.

A pixel includes at least one switching transistor 312 and a storagecapacitor that is not illustrated. A comb-shaped second electrode 352and a comb-shaped first electrode 343 electrically connected to one of asource electrode and a drain electrode of the transistor 312 areprovided apart from each other over the insulating layer 142.

For at least one of the first electrode 343 and the second electrode352, any of the above-described light-transmitting conductive materialsis used. It is preferable to use a light-transmitting conductivematerial for both of these electrodes because the aperture ratio of thepixel can be increased

Although the first electrode 343 and the second electrode 352 aredistinguished from each other in FIG. 13B by using different hatchpatterns, these electrodes are preferably formed by processing the sameconductive film.

A color filter 327 is provided at a position overlapping with the firstelectrode 343 and the second electrode 352. The color filter 327 isprovided over the insulating layer 141 in FIG. 13B, but the position ofthe color filter is not limited to this position.

A liquid crystal 353 is provided between the buffer layer 120 and eachof the first electrode 343 and the second electrode 352. An image can bedisplayed in the following way: voltage is applied between the firstelectrode 343 and the second electrode 352 to generate an electric fieldin the horizontal direction, orientation of the liquid crystal 353 iscontrolled by the electric field, and polarization of light from abacklight provided outside the display device is controlled in eachpixel.

Alignment films for controlling the orientation of the liquid crystal353 are preferably provided on surfaces in contact with the liquidcrystal 353. A light-transmitting material is used for the alignmentfilms. Although not illustrated here, polarizing plates are provided onthe surfaces of the first substrate 121 and the second substrate 101that do not face the liquid crystal element 314.

As the liquid crystal 353, a thermotropic liquid crystal, alow-molecular liquid crystal, a high-molecular liquid crystal, aferroelectric liquid crystal, an anti-ferroelectric liquid crystal, orthe like can be used. Moreover, a liquid crystal exhibiting a blue phaseis preferably used, in which case an alignment film is not needed and awide viewing angle can be obtained.

A high-viscosity and low-fluidity material is preferably used for theliquid crystal 353.

Although the liquid crystal element 314 using an IPS mode is describedhere as an example, the mode of the liquid crystal element is notlimited to this, and a twisted nematic (TN) mode, a fringe fieldswitching (FFS) mode, an axially symmetric aligned micro-cell (ASM)mode, an optically compensated birefringence (OCB) mode, a ferroelectricliquid crystal (FLC) mode, an antiferroelectric liquid crystal (AFLC)mode, or the like can be used.

The transistors (a transistor 311 and the transistor 312) in the displaydevice 300 are top-gate transistors. Each of the transistors includes asemiconductor layer 335 having an impurity region serving as a source ordrain region, an insulating layer 334 serving as a gate insulatinglayer, and a gate electrode 333. In addition, an insulating layer 338and an insulating layer 339 are stacked to cover the gate electrode 333.A pair of electrodes 336 are provided so as to reach the source or drainregion of the semiconductor layer 335 through an opening formed in theinsulating layers 334, 338, and 339.

In FIGS. 13A and 13B, the crack inhibiting region 110 is provided closerto the display portion 102 than the sealant 154 is. When the crackinhibiting region 110 is thus provided sufficiently apart from thedisplay portion 102, a crack generated in an end portion of the bufferlayer 120 can be prevented from developing across the display portion102, causing less misalignment of the liquid crystal element 314 and thelike due to the entry of impurities such as moisture. Note that thecrack inhibiting region 110 can also be provided outside the sealant 154as in Embodiment 1.

Note that the top-gate transistor described here can be replaced withthe bottom-gate transistor described in Embodiment 1. Alternatively, thetransistor described in Embodiment 1 can be replaced with the top-gatetransistor described here.

Note that for a display device of one embodiment of the presentinvention, an active matrix method in which an active element isincluded in a pixel or a passive matrix method in which an activeelement is not included in a pixel can be used.

In the active matrix method, as an active element (a non-linearelement), not only a transistor but also various active elements(non-linear elements) can be used. For example, a metal insulator metal(MIM) or a thin film diode (TFD) can be used. Such an element has fewnumbers of manufacturing steps; thus, the manufacturing cost can bereduced or yield can be improved. Furthermore, because the size of theelement is small, the aperture ratio can be improved, leading to lowerpower consumption or higher luminance.

As a method other than the active matrix method, the passive matrixmethod in which an active element (a non-linear element) is not used maybe used. Since an active element (a non-linear element) is not used, thenumber of manufacturing steps is small, so that the manufacturing costcan be reduced or yield can be improved. Furthermore, since an activeelement (a non-linear element) is not used, the aperture ratio can beimproved, leading to lower power consumption or higher luminance.

At least part of this embodiment can be implemented in an appropriatecombination with the other embodiments described in this specification.

Embodiment 4

In this embodiment, structure examples of a light-emitting device willbe described.

[Structure Example of Display Device]

FIGS. 14A to 14C illustrate examples of a flexible light-emitting deviceincluding an organic EL element as a light-emitting element.

FIG. 14A is a schematic top view of a light-emitting device 400. FIG.14B is a schematic cross-sectional view along line X1-Y1 in FIG. 14A.FIGS. 14A and 14B illustrate bottom-emission light-emitting devices.

As illustrated in FIG. 14B, the light-emitting device 400 includes asecond substrate 419, a bonding layer 422, a second buffer layer 424, aconductive layer 406, a conductive layer 416, an insulating layer 405, alight-emitting element 450 (a first electrode 401, an EL layer 402, anda second electrode 403), a sealing layer 407, a crack inhibiting layer410, a buffer layer 420, and a first substrate 428. The first electrode401, the second buffer layer 424, the bonding layer 422, and the secondsubstrate 419 transmit visible light. The first substrate 428 and thesecond substrate 419 are preferably flexible substrates.

The crack inhibiting layer 410 is provided so as to be in contact withthe buffer layer 420 and surround the light-emitting element 450. Whenthe crack inhibiting layer 410 is thus provided sufficiently apart fromthe light-emitting element 450, a crack generated in an end portion ofthe buffer layer 420 can be prevented from developing. This reduces theentry of impurities such as moisture into the light-emitting element450, whereby a highly reliable light-emitting device 400 can beprovided.

The light-emitting element 450 is provided over the second substrate 419with the bonding layer 422 and the second buffer layer 424 therebetween.The light-emitting element 450 is sealed by the second substrate 419,the sealing layer 407, and the first substrate 428. The light-emittingelement 450 includes the first electrode 401, the EL layer 402 over thefirst electrode 401, and the second electrode 403 over the EL layer 402.It is preferable that the second electrode 403 reflect visible light.

End portions of the first electrode 401, the conductive layer 406, andthe conductive layer 416 are covered with the insulating layer 405. Theconductive layer 406 is electrically connected to the first electrode401, and the conductive layer 416 is electrically connected to thesecond electrode 403. The conductive layer 406 covered with theinsulating layer 405 with the first electrode 401 therebetween iselectrically connected to the first electrode 401 and thereforefunctions as an auxiliary wiring. It is preferable that the electrode ofthe EL element include the auxiliary wiring, in which case a voltagedrop due to the electrical resistance of the electrode can be inhibited.Note that the conductive layer 406 may be provided over the firstelectrode 401. Furthermore, an auxiliary wiring that is electricallyconnected to the second electrode 403 may be provided, for example, overthe insulating layer 405.

To increase the outcoupling efficiency of the light-emitting device, alight outcoupling structure is preferably provided on the side fromwhich light emitted from the light-emitting element 450 is extracted.FIG. 14B illustrates an example in which the second substrate 419 fromwhich the light emitted from the light-emitting element 450 is extractedalso serves as the light outcoupling structure. Note that a touch sensoror the light outcoupling structure such as a sheet having a function ofdiffusing light may be provided so as to overlap with the secondsubstrate 419. Moreover, a polarizing plate or a retardation plate maybe provided. FIG. 14C illustrates a case where a diffusion plate 411 anda touch sensor 413 are provided so as to overlap with the secondsubstrate 419.

At least part of this embodiment can be implemented in an appropriatecombination with the other embodiments described in this specification.

Embodiment 5

In this embodiment, electronic devices and lighting devices that caninclude the light-emitting device or the display device of oneembodiment of the present invention will be described with reference toFIGS. 15A to 15C, FIGS. 16A to 161, and FIGS. 17A to 17C.

The display device of one embodiment of the present invention has abendable display surface. Examples of such a display device include atelevision set (also referred to as television or television receiver),a monitor of a computer, a camera such as a digital camera or a digitalvideo camera, a digital photo frame, a mobile phone set (also referredto as cellular phone or mobile phone device), a portable game machine, aportable information terminal, an audio reproducing device, and a largegame machine such as a pachinko machine.

In addition, a lighting device or a display device can be incorporatedalong a curved inside/outside wall surface of a house or a building or acurved interior/exterior surface of a car.

FIG. 15A illustrates an example of a cellular phone. A cellular phone7100 includes a display portion 7102 incorporated in a housing 7101,operation buttons 7103, an external connection port 7104, a speaker7105, a microphone 7106, a camera 7107, and the like. Note that thecellular phone 7100 is manufactured using the display device of oneembodiment of the present invention for the display portion 7102.

When the display portion 7102 of the cellular phone 7100 illustrated inFIG. 15A is touched with a finger or the like, data can be input intothe cellular phone 7100. Moreover, operations such as making a call andinputting a letter can be performed by touch on the display portion 7102with a finger or the like. For example, by touching an icon 7108displayed on the display portion 7102, application can be started.

With the operation buttons 7103, power on or off can be switched. Inaddition, a variety of images displayed on the display portion 7102 canbe switched, for example, from a mail creation screen to a main menuscreen.

Here, the display portion 7102 includes the display device of oneembodiment of the present invention. Thus, a highly reliable cellularphone having a curved display portion can be provided.

FIG. 15B is an example of a wristband-type display device. A portabledisplay device 7200 includes a housing 7201, a display portion 7202,operation buttons 7203, and a sending and receiving device 7204.

The portable display device 7200 can receive a video signal with thesending and receiving device 7204 and can display the received video onthe display portion 7202. In addition, with the sending and receivingdevice 7204, the portable display device 7200 can send an audio signalto another receiving device.

With the operation buttons 7203, power on/off, switching of displayedvideos, adjusting volume, and the like can be performed.

Here, the display portion 7202 includes the display device of oneembodiment of the present invention. Thus, a highly reliable portabledisplay device having a curved display portion can be provided.

FIG. 15C illustrates an example of a wrist-watch-type portableinformation terminal. A portable information terminal 7300 includes ahousing 7301, a display portion 7302, a band 7303, a buckle 7304, anoperation button 7305, an input/output terminal 7306, and the like.

The portable information terminal 7300 is capable of executing a varietyof applications such as mobile phone calls, e-mailing, reading andediting texts, music reproduction, Internet communication, and acomputer game.

The display surface of the display portion 7302 is bent, and images canbe displayed on the bent display surface. Furthermore, the displayportion 7302 includes a touch sensor, and operation can be performed bytouching the screen with a finger, a stylus, or the like. For example,by touching an icon 7307 displayed on the display portion 7302, anapplication can be started.

With the operation button 7305, a variety of functions such as timesetting, power on/off, on/off of wireless communication, setting andcancellation of manner mode, and setting and cancellation of powersaving mode can be performed. For example, the functions of theoperation button 7305 can be set freely by setting the operation systemincorporated in the portable information terminal 7300.

The portable information terminal 7300 can employ near fieldcommunication that is a communication method based on an existingcommunication standard. In that case, for example, mutual communicationbetween the portable information terminal 7300 and a headset capable ofwireless communication can be performed, and thus hands-free calling ispossible.

Moreover, the portable information terminal 7300 includes theinput/output terminal 7306, and data can be directly transmitted to andreceived from another information terminal via a connector. Chargingthrough the input/output terminal 7306 is also possible. Note that thecharging operation may be performed by wireless power feeding withoutusing the input/output terminal 7306.

The display device of one embodiment of the present invention can beused for the display portion 7302 of the portable information terminal7300. Thus, a highly reliable portable information terminal having acurved display portion can be provided.

FIGS. 16A to 16C illustrate a foldable portable information terminal7410. FIG. 16A illustrates the portable information terminal 7410 thatis opened. FIG. 16B illustrates the portable information terminal 7410that is being opened or being folded. FIG. 16C illustrates the portableinformation terminal 7410 that is folded. The portable informationterminal 7410 is highly portable when folded. The portable informationterminal 7410 is highly browsable when opened because of its seamlesslarge display region.

A display panel 7412 is supported by three housings 7415 joined togetherby hinges 7413. By folding the portable information terminal 7410 at aconnection portion between two housings 7415 with the hinges 7413, theportable information terminal 7410 can be reversibly changed in shapefrom an opened state to a folded state. A display device fabricated byemploying one embodiment of the present invention can be used for thedisplay panel 7412. For example, a display device that can be bent witha radius of curvature of greater than or equal to 1 mm and less than orequal to 150 mm can be used.

FIGS. 16D and 16E each illustrate a foldable portable informationterminal 7420. FIG. 16D illustrates the portable information terminal7420 that is folded so that a display portion 7422 is on the outside.FIG. 16E illustrates the portable information terminal 7420 that isfolded so that the display portion 7422 is on the inside. When theportable information terminal 7420 is not used, the portable informationterminal 7420 is folded so that a non-display portion 7425 faces theoutside, whereby the display portion 7422 can be prevented from beingcontaminated or damaged. A display device formed by employing oneembodiment of the present invention can be used for the display portion7422.

FIG. 16F is a perspective view illustrating an external shape of theportable information terminal 7430. FIG. 16G is a top view of theportable information terminal 7430. FIG. 16H is a perspective viewillustrating an external shape of a portable information terminal 7440.

The portable information terminals 7430 and 7440 each function as, forexample, one or more of a telephone set, a notebook, and an informationbrowsing system. Specifically, the portable information terminals 7430and 7440 each can be used as a smartphone.

The portable information terminals 7430 and 7440 can display charactersand image information on its plurality of surfaces. For example, threeoperation buttons 7439 can be displayed on one surface (FIGS. 16F and16H). In addition, information 7437 indicated by dashed rectangles canbe displayed on another surface (FIGS. 16G and 16H). Examples of theinformation 7437 include notification from a social networking service(SNS), display indicating reception of an e-mail or an incoming call,the title of an e-mail or the like, the sender of an e-mail or the like,the date, the time, remaining battery, and the reception strength of anantenna. Alternatively, the operation buttons 7439, an icon, or the likemay be displayed in place of the information 7437. Although FIGS. 16Fand 16G illustrate an example in which the information 7437 is displayedat the top, one embodiment of the present invention is not limitedthereto. The information may be displayed on the side, for example, asin the portable information terminal 7440 illustrated in FIG. 16H.

For example, a user of the portable information terminal 7430 can seethe display (here, the information 7437) with the portable informationterminal 7430 put in a breast pocket of his/her clothes.

Specifically, a caller's phone number, name, or the like of an incomingcall is displayed in a position that can be seen from above the portableinformation terminal 7430. Thus, the user can see the display withouttaking out the portable information terminal 7430 from the pocket anddecide whether to answer the call.

A display device fabricated by employing one embodiment of the presentinvention can be used for a display portion 7433 mounted in each of ahousing 7435 of the portable information terminal 7430 and a housing7436 of the portable information terminal 7440. Thus, a highly reliableportable information terminal having a curved display portion can beprovided.

As in a portable information terminal 7450 illustrated in FIG. 16I, datamay be displayed on three or more surfaces. Here, data 7455, data 7456,and data 7457 are displayed on different surfaces.

A display device fabricated by employing one embodiment of the presentinvention can be used for a display portion 7458 mounted in a housing7451 of the portable information terminal 7450. Thus, a highly reliableportable information terminal having a curved display portion can beprovided.

The display device of one embodiment of the present invention can beused in any of the display portions of the electronic devices describedin this embodiment. Accordingly, a highly reliable electronic devicethat has a curved display surface and has fewer defects due to bendingcan be achieved.

FIGS. 17A to 17C illustrate examples of a lighting device. Lightingdevices 8000, 8010, and 8020 each include a stage 8001 provided with anoperation switch 8003 and a light-emitting portion supported by thestage 8001.

The lighting device 8000 illustrated in FIG. 17A includes alight-emitting portion 8002 having a wave-shaped light-emitting surface,and thus has good design.

A light-emitting portion 8012 included in the lighting device 8010illustrated in FIG. 17B has two convex-curved light-emitting portionssymmetrically placed. Thus, light radiates from the lighting device 8010in all directions.

The lighting device 8020 illustrated in FIG. 17C includes aconcave-curved light-emitting portion 8022. This is suitable forilluminating a specific range because light emitted from thelight-emitting portion 8022 is collected to the front of the lightingdevice 8020.

The light-emitting portion included in each of the lighting devices8000, 8010, and 8020 are flexible; thus, the light-emitting portion maybe fixed on a plastic member, a movable frame, or the like so that anemission surface of the light-emitting portion can be bent freelydepending on the intended use.

Here, light-emitting portions 8002, 8012, and 8022 each include thelight-emitting device of one embodiment of the present invention. Thus,a highly reliable lighting device having a curved display portion can beprovided.

This embodiment can be implemented in an appropriate combination withthe other embodiments and example described in this specification.

Note that a content (or may be part of the content) described in oneembodiment may be applied to, combined with, or replaced by a differentcontent (or may be part of the different content) described in theembodiment and/or a content (or may be part of the content) described inone or a plurality of different embodiments.

Note that in each embodiment, a content described in the embodiment is acontent described with reference to a variety of diagrams or a contentdescribed with a text described in this specification.

Note that by combining a diagram (or may be part of the diagram)illustrated in one embodiment with another part of the diagram, adifferent diagram (or may be part of the different diagram) illustratedin the embodiment, and/or a diagram (or may be part of the diagram)illustrated in one or a plurality of different embodiments, much morediagrams can be formed.

Note that contents that are not specified in any drawing or text in thespecification can be excluded from one embodiment of the invention.Alternatively, when the range of a value that is defined by the maximumand minimum values is described, part of the range is appropriatelynarrowed or part of the range is removed, whereby one embodiment of theinvention excluding part of the range can be constituted. In thismanner, it is possible to specify the technical scope of one embodimentof the present invention so that a conventional technology is excluded,for example.

As a specific example, a diagram of a circuit including a firsttransistor to a fifth transistor is illustrated. In that case, it can bespecified that the circuit does not include a sixth transistor in theinvention. It can be specified that the circuit does not include acapacitor in the invention. It can be specified that the circuit doesnot include a sixth transistor with a particular connection structure inthe invention. It can be specified that the circuit does not include acapacitor with a particular connection structure in the invention. Forexample, it can be specified that a sixth transistor whose gate isconnected to a gate of the third transistor is not included in theinvention. For example, it can be specified that a capacitor whose firstelectrode is connected to the gate of the third transistor is notincluded in the invention.

As another specific example, a description of a value, “a voltage ispreferably higher than or equal to 3 V and lower than or equal to 10 V”is given. In that case, for example, it can be specified that the casewhere the voltage is higher than or equal to −2 V and lower than orequal to 1 V is excluded from one embodiment of the invention. Forexample, it can be specified that the case where the voltage is higherthan or equal to 13 V is excluded from one embodiment of the invention.Note that, for example, it can be specified that the voltage is higherthan or equal to 5 V and lower than or equal to 8 V in the invention.For example, it can be specified that the voltage is approximately 9 Vin the invention. For example, it can be specified that the voltage ishigher than or equal to 3 V and lower than or equal to 10 V but is not 9V in the invention. Note that even when the description “a value ispreferably in a certain range” or “a value preferably satisfies acertain condition” is given, the value is not limited to thedescription. In other words, a description of a value that includes aterm “preferable”, “preferably”, or the like does not necessarily limitthe value.

As another specific example, a description “a voltage is preferred to be10 V” is given. In that case, for example, it can be specified that thecase where the voltage is higher than or equal to −2 V and lower than orequal to 1 V is excluded from one embodiment of the invention. Forexample, it can be specified that the case where the voltage is higherthan or equal to 13 V is excluded from one embodiment of the invention.

As another specific example, a description “a film is an insulatingfilm” is given to describe properties of a material. In that case, forexample, it can be specified that the case where the insulating film isan organic insulating film is excluded from one embodiment of theinvention. For example, it can be specified that the case where theinsulating film is an inorganic insulating film is excluded from oneembodiment of the invention. For example, it can be specified that thecase where the insulating film is a conductive film is excluded from oneembodiment of the invention. For example, it can be specified that thecase where the insulating film is a semiconductor film is excluded fromone embodiment of the invention.

As another specific example, the description of a stacked structure, “afilm is provided between an A film and a B film” is given. In that case,for example, it can be specified that the case where the film is astacked film of four or more layers is excluded from the invention. Forexample, it can be specified that the case where a conductive film isprovided between the A film and the film is excluded from the invention.

Note that various people can implement one embodiment of the inventiondescribed in this specification and the like. However, different peoplemay be involved in the implementation of the invention. For example, inthe case of a transmission/reception system, the following case ispossible: Company A manufactures and sells transmitting devices, andCompany B manufactures and sells receiving devices. As another example,in the case of a light-emitting device including a transistor and alight-emitting element, the following case is possible: Company Amanufactures and sells semiconductor devices including transistors, andCompany B purchases the semiconductor devices, provides light-emittingelements for the semiconductor devices, and completes light-emittingdevices.

In such a case, one embodiment of the invention can be constituted sothat a patent infringement can be claimed against each of Company A andCompany B. In other words, one embodiment of the invention can beconstituted so that only Company A implements the embodiment, andanother embodiment of the invention can be constituted so that onlyCompany B implements the embodiment. One embodiment of the inventionwith which a patent infringement suit can be filed against Company A orCompany B is clear and can be regarded as being disclosed in thisspecification or the like. For example, in the case of atransmission/reception system, even when this specification or the likedoes not include a description of the case where a transmitting deviceis used alone or the case where a receiving device is used alone, oneembodiment of the invention can be constituted by only the transmittingdevice and another embodiment of the invention can be constituted byonly the receiving device. Those embodiments of the invention are clearand can be regarded as being disclosed in this specification or thelike. Another example is as follows: in the case of a light-emittingdevice including a transistor and a light-emitting element, even whenthis specification or the like does not include a description of thecase where a semiconductor device including the transistor is used aloneor the case where a light-emitting device including the light-emittingelement is used alone, one embodiment of the invention can beconstituted by only the semiconductor device including the transistorand another embodiment of the invention can be constituted by only thelight-emitting device including the light-emitting element. Thoseembodiments of the invention are clear and can be regarded as beingdisclosed in this specification or the like.

Note that in this specification and the like, it might be possible forthose skilled in the art to constitute one embodiment of the inventioneven when portions to which all the terminals of an active element(e.g., a transistor or a diode), a passive element (e.g., a capacitor ora resistor), or the like are connected are not specified. In otherwords, one embodiment of the invention can be clear even when connectionportions are not specified. Further, in the case where a connectionportion is disclosed in this specification and the like, it can bedetermined that one embodiment of the invention in which a connectionportion is not specified is disclosed in this specification and thelike, in some cases. In particular, in the case where the number ofportions to which the terminal is connected might be plural, it is notnecessary to specify the portions to which the terminal is connected.Therefore, it might be possible to constitute one embodiment of theinvention by specifying only portions to which some of terminals of anactive element (e.g., a transistor or a diode), a passive element (e.g.,a capacitor or a resistor), or the like are connected.

Note that in this specification and the like, it might be possible forthose skilled in the art to specify the invention when at least theconnection portion of a circuit is specified. Alternatively, it might bepossible for those skilled in the art to specify the invention when atleast a function of a circuit is specified. In other words, when afunction of a circuit is specified, one embodiment of the invention canbe clear. Furthermore, it can be determined that one embodiment of theinvention whose function is specified is disclosed in this specificationand the like. Therefore, when a connection portion of a circuit isspecified, the circuit is disclosed as one embodiment of the inventioneven when a function is not specified, and one embodiment of theinvention can be constituted. Alternatively, when a function of acircuit is specified, the circuit is disclosed as one embodiment of theinvention even when a connection portion is not specified, and oneembodiment of the invention can be constituted.

Note that in this specification and the like, in a diagram or a textdescribed in one embodiment, it is possible to take out part of thediagram or the text and constitute an embodiment of the invention. Thus,in the case where a diagram or a text related to a certain portion isdescribed, the context taken out from part of the diagram or the text isalso disclosed as one embodiment of the invention, and one embodiment ofthe invention can be constituted. The embodiment of the invention isclear. Therefore, for example, in a diagram or text in which one or moreactive elements (e.g., transistors or diodes), wirings, passive elements(e.g., capacitors or resistors), conductive layers, insulating layers,semiconductor layers, organic materials, inorganic materials,components, devices, operating methods, manufacturing methods, or thelike are described, part of the diagram or the text is taken out, andone embodiment of the invention can be constituted. For example, from acircuit diagram in which N circuit elements (e.g., transistors orcapacitors; N is an integer) are provided, it is possible to constituteone embodiment of the invention by taking out M circuit elements (e.g.,transistors or capacitors; M is an integer, where M<N). As anotherexample, it is possible to constitute one embodiment of the invention bytaking out M layers (M is an integer, where M<N) from a cross-sectionalview in which N layers (N is an integer) are provided. As anotherexample, it is possible to constitute one embodiment of the invention bytaking out M elements (M is an integer, where M<N) from a flow chart inwhich N elements (N is an integer) are provided. As another example, itis possible to take out some given elements from a sentence “A includesB, C, D, E, or F” and constitute one embodiment of the invention, forexample, “A includes B and E”, “A includes E and F”, “A includes C, E,and F”, or “A includes B, C, D, and E”.

Note that in the case where at least one specific example is describedin a diagram or a text described in one embodiment in this specificationand the like, it will be readily appreciated by those skilled in the artthat a broader concept of the specific example can be derived.Therefore, in the diagram or the text described in one embodiment, inthe case where at least one specific example is described, a broaderconcept of the specific example is disclosed as one embodiment of theinvention, and one embodiment of the invention can be constituted. Theembodiment of the invention is clear.

Note that in this specification and the like, a content described in atleast a diagram (which may be part of the diagram) is disclosed as oneembodiment of the invention, and one embodiment of the invention can beconstituted. Therefore, when a certain content is described in adiagram, the content is disclosed as one embodiment of the inventioneven when the content is not described with a text, and one embodimentof the invention can be constituted. In a similar manner, part of adiagram, which is taken out from the diagram, is disclosed as oneembodiment of the invention, and one embodiment of the invention can beconstituted. The embodiment of the invention is clear.

Example

In this example, a display device of one embodiment of the presentinvention was fabricated and subjected to a reliability test under ahigh temperature and high humidity environment. The results will bedescribed below.

In this example, a sample a, which is a display device of one embodimentof the present invention, and a sample b, which is a display device of acomparative example, were fabricated.

Note that the samples in this example were manufactured by the methodshown in Embodiment 1.

[Fabrication of Sample]

Materials used for the sample a and the comparative sample b will bedescribed with reference to FIG. 9.

A plastic film with a thickness of approximately 20 μm was used as thefirst substrate 121 and the second substrate 101.

A two-component epoxy resin was used for the bonding layers 125 and 131and the sealing layer 153.

Each of the buffer layer 120 and the second buffer layer 132 was formedusing a layered film of a silicon oxynitride film with a thickness ofapproximately 600 nm, a silicon nitride film with a thickness ofapproximately 200 nm, a silicon oxynitride film with a thickness ofapproximately 200 nm, a silicon nitride oxide film with a thickness ofapproximately 140 nm, and a silicon oxynitride film with a thickness ofapproximately 100 nm.

Only in the sample a, the crack inhibiting layer 122 was formed using atitanium film with a thickness of approximately 100 nm, and the coverlayer 123 was formed using an acrylic resin film with a thickness ofapproximately 2.0 μm.

The insulating layer 134 was formed using a layered film of a siliconnitride film with a thickness of approximately 400 nm and a siliconoxynitride film with a thickness of approximately 50 nm. The insulatinglayer 141 was formed using a layered film of a silicon oxynitride filmwith a thickness of approximately 450 nm and a silicon nitride film witha thickness of approximately 100 nm. An acrylic resin film with athickness of approximately 2.0 μm was used as the insulating layer 142.A polyimide resin film with a thickness of approximately 1.0 μm was usedas the insulating layer 144.

[Observation of Crack]

The sample a and the comparative sample b were subjected to areliability test; then, the crack inhibiting region and the vicinitythereof were observed with an optical microscope. In the reliabilitytest, the sample a and the comparative sample b were held in a hightemperature and high humidity environment (temperature: 65° C., andhumidity: 90%).

FIG. 18A and FIG. 19A show optical micrographs. FIG. 18B and FIG. 19Bare schematic cross-sectional views along lines X2-Y2 and X3-Y3,respectively.

FIG. 18A is an optical micrograph of the sample a that was held in thehigh temperature and high humidity environment for approximately 600hours. In the micrograph, a crack is generated from the top down, butthe development of the crack stops before the crack inhibiting region110.

FIG. 19A is an optical micrograph of the comparative sample b that washeld in the high temperature and high humidity environment forapproximately 600 hours. A crack is generated from the left of themicrograph and develops into the scan line driver circuit portion.

Another sample that is different from the comparative sample b only inthe material of the insulating layer 142 was fabricated and a crosssection thereof was observed. Then, a crack was found in the bufferlayer 120 (FIG. 20). The insulating layer 142 in this sample was formedusing a polyimide resin film with a thickness of approximately 2.0 μm.The above results indicate that the development of a crack generated inthe buffer layer 120 can be hindered by providing the crack inhibitingregion 110 in contact with the buffer layer 120.

As a result, the crack inhibiting layer on the outer edge of the displaydevice was found to be effective for preventing the development of acrack.

This application is based on Japanese Patent Application serial No.2014-043742 filed with Japan Patent Office on Mar. 6, 2014, the entirecontents of which are hereby incorporated by reference.

EXPLANATION OF REFERENCE

-   -   100: display device, 101: substrate, 102: display portion, 103:        signal line driver circuit, 104: scan line driver circuit, 105:        external connection terminal, 110: crack inhibiting region, 111:        transistor, 112: transistor, 113: transistor, 114:        light-emitting element, 115: crack inhibiting region, 120:        buffer layer, 120 a: buffer layer, 120 b: buffer layer, 121:        substrate, 122: crack inhibiting layer, 123: cover layer, 124:        marker, 125: bonding layer, 126: black matrix, 127: color        filter, 128: organic resin layer, 131: bonding layer, 132:        buffer layer, 133: gate electrode, 134: insulating layer, 135:        semiconductor layer, 136: electrode, 137: crack inhibiting        layer, 138: organic resin layer, 141: insulating layer, 142:        insulating layer, 143: electrode, 144: insulating layer, 145:        insulating layer, 151: EL layer, 152: electrode, 153: sealing        layer, 154: sealant, 155: FPC, 156: connector, 161: support        substrate, 162: separation layer, 163: support substrate, 164:        separation layer, 200: light-emitting module, 201: touch sensor,        210: crack inhibiting region, 220: buffer layer, 221: substrate,        222: crack inhibiting layer, 225: bonding layer, 231: wiring,        232: wiring, 233: insulating layer, 234: electrode, 235:        electrode, 236: insulating layer, 255: connector, 256: FPC, 300:        display device, 311: transistor, 312: transistor, 314: liquid        crystal element 327: color filter, 333: gate electrode, 334:        insulating layer, 335: semiconductor layer, 336: electrode, 338:        insulating layer, 339: insulating layer, 343: electrode, 352:        electrode, 353: liquid crystal, 400: light-emitting device, 401:        electrode, 402: EL layer, 403: electrode, 405: insulating layer,        406: conductive layer, 407: sealing layer, 410: crack inhibiting        layer, 411: diffusion plate, 413; touch sensor, 416: conductive        layer, 419: substrate, 420: buffer layer, 422: bonding layer,        424: buffer layer, 428: substrate, 450: light-emitting element,        7100: cellular phone, 7101: housing, 7102: display portion,        7103: operation button, 7104: external connection port, 7105:        speaker, 7106: microphone, 7107: camera, 7108: icon, 7200:        portable display device, 7201: housing, 7202: display portion,        7203: operation button, 7204: sending and receiving device,        7300: portable information terminal, 7301: housing, 7302:        display portion, 7303: band, 7304: buckle, 7305: operation        button, 7306: input/output terminal, 7307: icon, 7410: portable        information terminal, 7412: display panel, 7413: hinge, 7415:        housing, 7420: portable information terminal, 7422: display        portion, 7425: non-display portion, 7430: portable information        terminal, 7433: display portion, 7435: housing, 7436: housing,        7437: information, 7439: operation button, 7440: portable        information terminal, 7450: portable information terminal, 7451:        housing, 7455: data, 7456: data, 7457: data, 7458: display        portion, 8000: lighting device, 8001: stage, 8002:        light-emitting portion, 8003: operation switch, 8010: lighting        device, 8012: light-emitting portion, 8020: lighting device, and        8022: light-emitting portion.

1. A light-emitting device comprising a first flexible substrate, asecond flexible substrate, a first buffer layer, a first crackinhibiting layer, and a light-emitting element, wherein a first surfaceof the first flexible substrate faces a second surface of the secondflexible substrate, wherein the first buffer layer and the first crackinhibiting layer are provided over the first surface of the firstflexible substrate, wherein the first buffer layer overlaps with thefirst crack inhibiting layer, and wherein the light-emitting element isprovided over the second surface of the second flexible substrate. 2.The light-emitting device according to claim 1, wherein the first bufferlayer includes an inorganic material, wherein the light-emitting elementincludes a light-emitting organic compound, and wherein the first crackinhibiting layer includes a conductive material or a resin material andis positioned between the light-emitting element and an end portion ofthe first flexible substrate when seen from a direction perpendicular tothe first surface.
 3. The light-emitting device according to claim 1,wherein a first bonding layer is provided between the first flexiblesubstrate and the first buffer layer, and wherein a second bonding layerand a second buffer layer are provided between the second flexiblesubstrate and the light-emitting element.
 4. The light-emitting deviceaccording to claim 1, further comprising a layer provided over the firstsurface of the first flexible substrate, wherein the layer serves as amarker and includes the same material as the first crack inhibitinglayer.
 5. The light-emitting device according to claim 1, furthercomprising a light-blocking layer provided over the first surface of thefirst flexible substrate, wherein the light-blocking layer has afunction of blocking light from the light-emitting element and includesthe same material as the first crack inhibiting layer.
 6. Thelight-emitting device according to claim 1, further comprising a coverlayer provided over the first surface of the first flexible substrate,wherein the cover layer includes a portion covering the first crackinhibiting layer, and wherein the cover layer includes a conductivematerial or a resin material and is positioned between thelight-emitting element and an end portion of the first flexiblesubstrate when seen from a direction perpendicular to the first surface.7. The light-emitting device according to claim 1, wherein a secondcrack inhibiting layer is provided over the second surface of the secondflexible substrate, and wherein the second crack inhibiting layerincludes a conductive material or a resin material and is positionedbetween the light-emitting element and an end portion of the firstflexible substrate when seen from a direction perpendicular to the firstsurface.
 8. A light-emitting module comprising a touch sensor over athird surface of the first flexible substrate or a fourth surface of thesecond flexible substrate in the light-emitting device according toclaim 1, wherein the third surface is a surface opposite to the firstsurface of the first flexible substrate, and the fourth surface is asurface opposite to the second surface of the second flexible substrate.